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diff --git a/doc/tar.info-1 b/doc/tar.info-1 new file mode 100644 index 0000000..362a137 --- /dev/null +++ b/doc/tar.info-1 @@ -0,0 +1,7594 @@ +This is tar.info, produced by makeinfo version 4.8 from tar.texi. + + This manual is for GNU `tar' (version 1.17, 8 June 2007), which +creates and extracts files from archives. + + Copyright (C) 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001, 2003, +2004, 2005, 2006, 2007 Free Software Foundation, Inc. + + Permission is granted to copy, distribute and/or modify this + document under the terms of the GNU Free Documentation License, + Version 1.1 or any later version published by the Free Software + Foundation; with no Invariant Sections, with the Front-Cover Texts + being "A GNU Manual," and with the Back-Cover Texts as in (a) + below. A copy of the license is included in the section entitled + "GNU Free Documentation License". + + (a) The FSF's Back-Cover Text is: "You are free to copy and modify + this GNU Manual. Buying copies from GNU Press supports the FSF in + developing GNU and promoting software freedom." + +INFO-DIR-SECTION Archiving +START-INFO-DIR-ENTRY +* Tar: (tar). Making tape (or disk) archives. +END-INFO-DIR-ENTRY + +INFO-DIR-SECTION Individual utilities +START-INFO-DIR-ENTRY +* tar: (tar)tar invocation. Invoking GNU `tar'. +END-INFO-DIR-ENTRY + + +File: tar.info, Node: Top, Next: Introduction, Up: (dir) + +GNU tar: an archiver tool +************************* + +This manual is for GNU `tar' (version 1.17, 8 June 2007), which creates +and extracts files from archives. + + Copyright (C) 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001, 2003, +2004, 2005, 2006, 2007 Free Software Foundation, Inc. + + Permission is granted to copy, distribute and/or modify this + document under the terms of the GNU Free Documentation License, + Version 1.1 or any later version published by the Free Software + Foundation; with no Invariant Sections, with the Front-Cover Texts + being "A GNU Manual," and with the Back-Cover Texts as in (a) + below. A copy of the license is included in the section entitled + "GNU Free Documentation License". + + (a) The FSF's Back-Cover Text is: "You are free to copy and modify + this GNU Manual. Buying copies from GNU Press supports the FSF in + developing GNU and promoting software freedom." + + The first part of this master menu lists the major nodes in this Info +document. The rest of the menu lists all the lower level nodes. + +* Menu: + +* Introduction:: +* Tutorial:: +* tar invocation:: +* operations:: +* Backups:: +* Choosing:: +* Date input formats:: +* Formats:: +* Media:: + +Appendices + +* Changes:: +* Configuring Help Summary:: +* Tar Internals:: +* Genfile:: +* Free Software Needs Free Documentation:: +* Copying This Manual:: +* Index of Command Line Options:: +* Index:: + + --- The Detailed Node Listing --- + +Introduction + +* Book Contents:: What this Book Contains +* Definitions:: Some Definitions +* What tar Does:: What `tar' Does +* Naming tar Archives:: How `tar' Archives are Named +* Authors:: GNU `tar' Authors +* Reports:: Reporting bugs or suggestions + +Tutorial Introduction to `tar' + +* assumptions:: +* stylistic conventions:: +* basic tar options:: Basic `tar' Operations and Options +* frequent operations:: +* Two Frequent Options:: +* create:: How to Create Archives +* list:: How to List Archives +* extract:: How to Extract Members from an Archive +* going further:: + +Two Frequently Used Options + +* file tutorial:: +* verbose tutorial:: +* help tutorial:: + +How to Create Archives + +* prepare for examples:: +* Creating the archive:: +* create verbose:: +* short create:: +* create dir:: + +How to List Archives + +* list dir:: + +How to Extract Members from an Archive + +* extracting archives:: +* extracting files:: +* extract dir:: +* extracting untrusted archives:: +* failing commands:: + +Invoking GNU `tar' + +* Synopsis:: +* using tar options:: +* Styles:: +* All Options:: +* help:: +* defaults:: +* verbose:: +* interactive:: + +The Three Option Styles + +* Long Options:: Long Option Style +* Short Options:: Short Option Style +* Old Options:: Old Option Style +* Mixing:: Mixing Option Styles + +All `tar' Options + +* Operation Summary:: +* Option Summary:: +* Short Option Summary:: + +GNU `tar' Operations + +* Basic tar:: +* Advanced tar:: +* create options:: +* extract options:: +* backup:: +* Applications:: +* looking ahead:: + +Advanced GNU `tar' Operations + +* Operations:: +* append:: +* update:: +* concatenate:: +* delete:: +* compare:: + +How to Add Files to Existing Archives: `--append' + +* appending files:: Appending Files to an Archive +* multiple:: + +Updating an Archive + +* how to update:: + +Options Used by `--create' + +* override:: Overriding File Metadata. +* Ignore Failed Read:: + +Options Used by `--extract' + +* Reading:: Options to Help Read Archives +* Writing:: Changing How `tar' Writes Files +* Scarce:: Coping with Scarce Resources + +Options to Help Read Archives + +* read full records:: +* Ignore Zeros:: + +Changing How `tar' Writes Files + +* Dealing with Old Files:: +* Overwrite Old Files:: +* Keep Old Files:: +* Keep Newer Files:: +* Unlink First:: +* Recursive Unlink:: +* Data Modification Times:: +* Setting Access Permissions:: +* Directory Modification Times and Permissions:: +* Writing to Standard Output:: +* Writing to an External Program:: +* remove files:: + +Coping with Scarce Resources + +* Starting File:: +* Same Order:: + +Performing Backups and Restoring Files + +* Full Dumps:: Using `tar' to Perform Full Dumps +* Incremental Dumps:: Using `tar' to Perform Incremental Dumps +* Backup Levels:: Levels of Backups +* Backup Parameters:: Setting Parameters for Backups and Restoration +* Scripted Backups:: Using the Backup Scripts +* Scripted Restoration:: Using the Restore Script + +Setting Parameters for Backups and Restoration + +* General-Purpose Variables:: +* Magnetic Tape Control:: +* User Hooks:: +* backup-specs example:: An Example Text of `Backup-specs' + +Choosing Files and Names for `tar' + +* file:: Choosing the Archive's Name +* Selecting Archive Members:: +* files:: Reading Names from a File +* exclude:: Excluding Some Files +* wildcards:: Wildcards Patterns and Matching +* quoting styles:: Ways of Quoting Special Characters in Names +* transform:: Modifying File and Member Names +* after:: Operating Only on New Files +* recurse:: Descending into Directories +* one:: Crossing File System Boundaries + +Reading Names from a File + +* nul:: + +Excluding Some Files + +* problems with exclude:: + +Wildcards Patterns and Matching + +* controlling pattern-matching:: + +Crossing File System Boundaries + +* directory:: Changing Directory +* absolute:: Absolute File Names + +Date input formats + +* General date syntax:: Common rules. +* Calendar date items:: 19 Dec 1994. +* Time of day items:: 9:20pm. +* Time zone items:: EST, PDT, GMT. +* Day of week items:: Monday and others. +* Relative items in date strings:: next tuesday, 2 years ago. +* Pure numbers in date strings:: 19931219, 1440. +* Seconds since the Epoch:: @1078100502. +* Specifying time zone rules:: TZ="America/New_York", TZ="UTC0". +* Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al. + +Controlling the Archive Format + +* Portability:: Making `tar' Archives More Portable +* Compression:: Using Less Space through Compression +* Attributes:: Handling File Attributes +* cpio:: Comparison of `tar' and `cpio' + +Making `tar' Archives More Portable + +* Portable Names:: Portable Names +* dereference:: Symbolic Links +* old:: Old V7 Archives +* ustar:: Ustar Archives +* gnu:: GNU and old GNU format archives. +* posix:: POSIX archives +* Checksumming:: Checksumming Problems +* Large or Negative Values:: Large files, negative time stamps, etc. +* Other Tars:: How to Extract GNU-Specific Data Using + Other `tar' Implementations + +GNU `tar' and POSIX `tar' + +* PAX keywords:: Controlling Extended Header Keywords. + +How to Extract GNU-Specific Data Using Other `tar' Implementations + +* Split Recovery:: Members Split Between Volumes +* Sparse Recovery:: Sparse Members + +Using Less Space through Compression + +* gzip:: Creating and Reading Compressed Archives +* sparse:: Archiving Sparse Files + +Tapes and Other Archive Media + +* Device:: Device selection and switching +* Remote Tape Server:: +* Common Problems and Solutions:: +* Blocking:: Blocking +* Many:: Many archives on one tape +* Using Multiple Tapes:: Using Multiple Tapes +* label:: Including a Label in the Archive +* verify:: +* Write Protection:: + +Blocking + +* Format Variations:: Format Variations +* Blocking Factor:: The Blocking Factor of an Archive + +Many Archives on One Tape + +* Tape Positioning:: Tape Positions and Tape Marks +* mt:: The `mt' Utility + +Using Multiple Tapes + +* Multi-Volume Archives:: Archives Longer than One Tape or Disk +* Tape Files:: Tape Files +* Tarcat:: Concatenate Volumes into a Single Archive + + +Tar Internals + +* Standard:: Basic Tar Format +* Extensions:: GNU Extensions to the Archive Format +* Sparse Formats:: Storing Sparse Files +* Snapshot Files:: +* Dumpdir:: + +Storing Sparse Files + +* Old GNU Format:: +* PAX 0:: PAX Format, Versions 0.0 and 0.1 +* PAX 1:: PAX Format, Version 1.0 + +Genfile + +* Generate Mode:: File Generation Mode. +* Status Mode:: File Status Mode. +* Exec Mode:: Synchronous Execution mode. + +Copying This Manual + +* GNU Free Documentation License:: License for copying this manual + + +File: tar.info, Node: Introduction, Next: Tutorial, Prev: Top, Up: Top + +1 Introduction +************** + +GNU `tar' creates and manipulates "archives" which are actually +collections of many other files; the program provides users with an +organized and systematic method for controlling a large amount of data. +The name "tar" originally came from the phrase "Tape ARchive", but +archives need not (and these days, typically do not) reside on tapes. + +* Menu: + +* Book Contents:: What this Book Contains +* Definitions:: Some Definitions +* What tar Does:: What `tar' Does +* Naming tar Archives:: How `tar' Archives are Named +* Authors:: GNU `tar' Authors +* Reports:: Reporting bugs or suggestions + + +File: tar.info, Node: Book Contents, Next: Definitions, Up: Introduction + +1.1 What this Book Contains +=========================== + +The first part of this chapter introduces you to various terms that will +recur throughout the book. It also tells you who has worked on GNU +`tar' and its documentation, and where you should send bug reports or +comments. + + The second chapter is a tutorial (*note Tutorial::) which provides a +gentle introduction for people who are new to using `tar'. It is meant +to be self contained, not requiring any reading from subsequent +chapters to make sense. It moves from topic to topic in a logical, +progressive order, building on information already explained. + + Although the tutorial is paced and structured to allow beginners to +learn how to use `tar', it is not intended solely for beginners. The +tutorial explains how to use the three most frequently used operations +(`create', `list', and `extract') as well as two frequently used +options (`file' and `verbose'). The other chapters do not refer to the +tutorial frequently; however, if a section discusses something which is +a complex variant of a basic concept, there may be a cross reference to +that basic concept. (The entire book, including the tutorial, assumes +that the reader understands some basic concepts of using a Unix-type +operating system; *note Tutorial::.) + + The third chapter presents the remaining five operations, and +information about using `tar' options and option syntax. + + The other chapters are meant to be used as a reference. Each +chapter presents everything that needs to be said about a specific +topic. + + One of the chapters (*note Date input formats::) exists in its +entirety in other GNU manuals, and is mostly self-contained. In +addition, one section of this manual (*note Standard::) contains a big +quote which is taken directly from `tar' sources. + + In general, we give both long and short (abbreviated) option names +at least once in each section where the relevant option is covered, so +that novice readers will become familiar with both styles. (A few +options have no short versions, and the relevant sections will indicate +this.) + + +File: tar.info, Node: Definitions, Next: What tar Does, Prev: Book Contents, Up: Introduction + +1.2 Some Definitions +==================== + +The `tar' program is used to create and manipulate `tar' archives. An +"archive" is a single file which contains the contents of many files, +while still identifying the names of the files, their owner(s), and so +forth. (In addition, archives record access permissions, user and +group, size in bytes, and data modification time. Some archives also +record the file names in each archived directory, as well as other file +and directory information.) You can use `tar' to "create" a new +archive in a specified directory. + + The files inside an archive are called "members". Within this +manual, we use the term "file" to refer only to files accessible in the +normal ways (by `ls', `cat', and so forth), and the term "member" to +refer only to the members of an archive. Similarly, a "file name" is +the name of a file, as it resides in the file system, and a "member +name" is the name of an archive member within the archive. + + The term "extraction" refers to the process of copying an archive +member (or multiple members) into a file in the file system. Extracting +all the members of an archive is often called "extracting the archive". +The term "unpack" can also be used to refer to the extraction of many +or all the members of an archive. Extracting an archive does not +destroy the archive's structure, just as creating an archive does not +destroy the copies of the files that exist outside of the archive. You +may also "list" the members in a given archive (this is often thought +of as "printing" them to the standard output, or the command line), or +"append" members to a pre-existing archive. All of these operations +can be performed using `tar'. + + +File: tar.info, Node: What tar Does, Next: Naming tar Archives, Prev: Definitions, Up: Introduction + +1.3 What `tar' Does +=================== + +The `tar' program provides the ability to create `tar' archives, as +well as various other kinds of manipulation. For example, you can use +`tar' on previously created archives to extract files, to store +additional files, or to update or list files which were already stored. + + Initially, `tar' archives were used to store files conveniently on +magnetic tape. The name `tar' comes from this use; it stands for +`t'ape `ar'chiver. Despite the utility's name, `tar' can direct its +output to available devices, files, or other programs (using pipes). +`tar' may even access remote devices or files (as archives). + + You can use `tar' archives in many ways. We want to stress a few of +them: storage, backup, and transportation. + +Storage + Often, `tar' archives are used to store related files for + convenient file transfer over a network. For example, the GNU + Project distributes its software bundled into `tar' archives, so + that all the files relating to a particular program (or set of + related programs) can be transferred as a single unit. + + A magnetic tape can store several files in sequence. However, the + tape has no names for these files; it only knows their relative + position on the tape. One way to store several files on one tape + and retain their names is by creating a `tar' archive. Even when + the basic transfer mechanism can keep track of names, as FTP can, + the nuisance of handling multiple files, directories, and multiple + links makes `tar' archives useful. + + Archive files are also used for long-term storage. You can think + of this as transportation from the present into the future. (It + is a science-fiction idiom that you can move through time as well + as in space; the idea here is that `tar' can be used to move + archives in all dimensions, even time!) + +Backup + Because the archive created by `tar' is capable of preserving file + information and directory structure, `tar' is commonly used for + performing full and incremental backups of disks. A backup puts a + collection of files (possibly pertaining to many users and + projects) together on a disk or a tape. This guards against + accidental destruction of the information in those files. GNU + `tar' has special features that allow it to be used to make + incremental and full dumps of all the files in a file system. + +Transportation + You can create an archive on one system, transfer it to another + system, and extract the contents there. This allows you to + transport a group of files from one system to another. + + +File: tar.info, Node: Naming tar Archives, Next: Authors, Prev: What tar Does, Up: Introduction + +1.4 How `tar' Archives are Named +================================ + +Conventionally, `tar' archives are given names ending with `.tar'. +This is not necessary for `tar' to operate properly, but this manual +follows that convention in order to accustom readers to it and to make +examples more clear. + + Often, people refer to `tar' archives as "`tar' files," and archive +members as "files" or "entries". For people familiar with the +operation of `tar', this causes no difficulty. However, in this +manual, we consistently refer to "archives" and "archive members" to +make learning to use `tar' easier for novice users. + + +File: tar.info, Node: Authors, Next: Reports, Prev: Naming tar Archives, Up: Introduction + +1.5 GNU `tar' Authors +===================== + +GNU `tar' was originally written by John Gilmore, and modified by many +people. The GNU enhancements were written by Jay Fenlason, then Joy +Kendall, and the whole package has been further maintained by Thomas +Bushnell, n/BSG, Franc,ois Pinard, Paul Eggert, and finally Sergey +Poznyakoff with the help of numerous and kind users. + + We wish to stress that `tar' is a collective work, and owes much to +all those people who reported problems, offered solutions and other +insights, or shared their thoughts and suggestions. An impressive, yet +partial list of those contributors can be found in the `THANKS' file +from the GNU `tar' distribution. + + Jay Fenlason put together a draft of a GNU `tar' manual, borrowing +notes from the original man page from John Gilmore. This was withdrawn +in version 1.11. Thomas Bushnell, n/BSG and Amy Gorin worked on a +tutorial and manual for GNU `tar'. Franc,ois Pinard put version 1.11.8 +of the manual together by taking information from all these sources and +merging them. Melissa Weisshaus finally edited and redesigned the book +to create version 1.12. The book for versions from 1.14 up to 1.17 +were edited by the current maintainer, Sergey Poznyakoff. + + For version 1.12, Daniel Hagerty contributed a great deal of +technical consulting. In particular, he is the primary author of *note +Backups::. + + In July, 2003 GNU `tar' was put on CVS at savannah.gnu.org (see +`http://savannah.gnu.org/projects/tar'), and active development and +maintenance work has started again. Currently GNU `tar' is being +maintained by Paul Eggert, Sergey Poznyakoff and Jeff Bailey. + + Support for POSIX archives was added by Sergey Poznyakoff. + + +File: tar.info, Node: Reports, Prev: Authors, Up: Introduction + +1.6 Reporting bugs or suggestions +================================= + +If you find problems or have suggestions about this program or manual, +please report them to `bug-tar@gnu.org'. + + When reporting a bug, please be sure to include as much detail as +possible, in order to reproduce it. . + + +File: tar.info, Node: Tutorial, Next: tar invocation, Prev: Introduction, Up: Top + +2 Tutorial Introduction to `tar' +******************************** + +This chapter guides you through some basic examples of three `tar' +operations: `--create', `--list', and `--extract'. If you already know +how to use some other version of `tar', then you may not need to read +this chapter. This chapter omits most complicated details about how +`tar' works. + +* Menu: + +* assumptions:: +* stylistic conventions:: +* basic tar options:: Basic `tar' Operations and Options +* frequent operations:: +* Two Frequent Options:: +* create:: How to Create Archives +* list:: How to List Archives +* extract:: How to Extract Members from an Archive +* going further:: + + +File: tar.info, Node: assumptions, Next: stylistic conventions, Up: Tutorial + +2.1 Assumptions this Tutorial Makes +=================================== + +This chapter is paced to allow beginners to learn about `tar' slowly. +At the same time, we will try to cover all the basic aspects of these +three operations. In order to accomplish both of these tasks, we have +made certain assumptions about your knowledge before reading this +manual, and the hardware you will be using: + + * Before you start to work through this tutorial, you should + understand what the terms "archive" and "archive member" mean + (*note Definitions::). In addition, you should understand + something about how Unix-type operating systems work, and you + should know how to use some basic utilities. For example, you + should know how to create, list, copy, rename, edit, and delete + files and directories; how to change between directories; and how + to figure out where you are in the file system. You should have + some basic understanding of directory structure and how files are + named according to which directory they are in. You should + understand concepts such as standard output and standard input, + what various definitions of the term "argument" mean, and the + differences between relative and absolute file names. + + * This manual assumes that you are working from your own home + directory (unless we state otherwise). In this tutorial, you will + create a directory to practice `tar' commands in. When we show + file names, we will assume that those names are relative to your + home directory. For example, my home directory is + `/home/fsf/melissa'. All of my examples are in a subdirectory of + the directory named by that file name; the subdirectory is called + `practice'. + + * In general, we show examples of archives which exist on (or can be + written to, or worked with from) a directory on a hard disk. In + most cases, you could write those archives to, or work with them + on any other device, such as a tape drive. However, some of the + later examples in the tutorial and next chapter will not work on + tape drives. Additionally, working with tapes is much more + complicated than working with hard disks. For these reasons, the + tutorial does not cover working with tape drives. *Note Media::, + for complete information on using `tar' archives with tape drives. + + + +File: tar.info, Node: stylistic conventions, Next: basic tar options, Prev: assumptions, Up: Tutorial + +2.2 Stylistic Conventions +========================= + +In the examples, `$' represents a typical shell prompt. It precedes +lines you should type; to make this more clear, those lines are shown +in `this font', as opposed to lines which represent the computer's +response; those lines are shown in `this font', or sometimes `like +this'. + + +File: tar.info, Node: basic tar options, Next: frequent operations, Prev: stylistic conventions, Up: Tutorial + +2.3 Basic `tar' Operations and Options +====================================== + +`tar' can take a wide variety of arguments which specify and define the +actions it will have on the particular set of files or the archive. +The main types of arguments to `tar' fall into one of two classes: +operations, and options. + + Some arguments fall into a class called "operations"; exactly one of +these is both allowed and required for any instance of using `tar'; you +may _not_ specify more than one. People sometimes speak of "operating +modes". You are in a particular operating mode when you have specified +the operation which specifies it; there are eight operations in total, +and thus there are eight operating modes. + + The other arguments fall into the class known as "options". You are +not required to specify any options, and you are allowed to specify more +than one at a time (depending on the way you are using `tar' at that +time). Some options are used so frequently, and are so useful for +helping you type commands more carefully that they are effectively +"required". We will discuss them in this chapter. + + You can write most of the `tar' operations and options in any of +three forms: long (mnemonic) form, short form, and old style. Some of +the operations and options have no short or "old" forms; however, the +operations and options which we will cover in this tutorial have +corresponding abbreviations. We will indicate those abbreviations +appropriately to get you used to seeing them. (Note that the "old +style" option forms exist in GNU `tar' for compatibility with Unix +`tar'. In this book we present a full discussion of this way of +writing options and operations (*note Old Options::), and we discuss +the other two styles of writing options (*Note Long Options::, and +*note Short Options::). + + In the examples and in the text of this tutorial, we usually use the +long forms of operations and options; but the "short" forms produce the +same result and can make typing long `tar' commands easier. For +example, instead of typing + + tar --create --verbose --file=afiles.tar apple angst aspic + +you can type + tar -c -v -f afiles.tar apple angst aspic + +or even + tar -cvf afiles.tar apple angst aspic + +For more information on option syntax, see *note Advanced tar::. In +discussions in the text, when we name an option by its long form, we +also give the corresponding short option in parentheses. + + The term, "option", can be confusing at times, since "operations" +are often lumped in with the actual, _optional_ "options" in certain +general class statements. For example, we just talked about "short and +long forms of options and operations". However, experienced `tar' +users often refer to these by shorthand terms such as, "short and long +options". This term assumes that the "operations" are included, also. +Context will help you determine which definition of "options" to use. + + Similarly, the term "command" can be confusing, as it is often used +in two different ways. People sometimes refer to `tar' "commands". A +`tar' "command" is the entire command line of user input which tells +`tar' what to do -- including the operation, options, and any arguments +(file names, pipes, other commands, etc.). However, you will also +sometimes hear the term "the `tar' command". When the word "command" +is used specifically like this, a person is usually referring to the +`tar' _operation_, not the whole line. Again, use context to figure +out which of the meanings the speaker intends. + + +File: tar.info, Node: frequent operations, Next: Two Frequent Options, Prev: basic tar options, Up: Tutorial + +2.4 The Three Most Frequently Used Operations +============================================= + +Here are the three most frequently used operations (both short and long +forms), as well as a brief description of their meanings. The rest of +this chapter will cover how to use these operations in detail. We will +present the rest of the operations in the next chapter. + +`--create' +`-c' + Create a new `tar' archive. + +`--list' +`-t' + List the contents of an archive. + +`--extract' +`-x' + Extract one or more members from an archive. + + +File: tar.info, Node: Two Frequent Options, Next: create, Prev: frequent operations, Up: Tutorial + +2.5 Two Frequently Used Options +=============================== + +To understand how to run `tar' in the three operating modes listed +previously, you also need to understand how to use two of the options to +`tar': `--file' (which takes an archive file as an argument) and +`--verbose'. (You are usually not _required_ to specify either of +these options when you run `tar', but they can be very useful in making +things more clear and helping you avoid errors.) + +* Menu: + +* file tutorial:: +* verbose tutorial:: +* help tutorial:: + + +File: tar.info, Node: file tutorial, Next: verbose tutorial, Up: Two Frequent Options + +The `--file' Option +------------------- + +`--file=ARCHIVE-NAME' +`-f ARCHIVE-NAME' + Specify the name of an archive file. + + You can specify an argument for the `--file=ARCHIVE-NAME' (`-f +ARCHIVE-NAME') option whenever you use `tar'; this option determines +the name of the archive file that `tar' will work on. + + If you don't specify this argument, then `tar' will examine the +environment variable `TAPE'. If it is set, its value will be used as +the archive name. Otherwise, `tar' will use the default archive, +determined at the compile time. Usually it is standard output or some +physical tape drive attached to your machine (you can verify what the +default is by running `tar --show-defaults', *note defaults::). If +there is no tape drive attached, or the default is not meaningful, then +`tar' will print an error message. The error message might look +roughly like one of the following: + + tar: can't open /dev/rmt8 : No such device or address + tar: can't open /dev/rsmt0 : I/O error + +To avoid confusion, we recommend that you always specify an archive file +name by using `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') when writing +your `tar' commands. For more information on using the +`--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') option, see *note file::. + + +File: tar.info, Node: verbose tutorial, Next: help tutorial, Prev: file tutorial, Up: Two Frequent Options + +The `--verbose' Option +---------------------- + +`--verbose' +`-v' + Show the files being worked on as `tar' is running. + + `--verbose' (`-v') shows details about the results of running `tar'. +This can be especially useful when the results might not be obvious. +For example, if you want to see the progress of `tar' as it writes +files into the archive, you can use the `--verbose' option. In the +beginning, you may find it useful to use `--verbose' at all times; when +you are more accustomed to `tar', you will likely want to use it at +certain times but not at others. We will use `--verbose' at times to +help make something clear, and we will give many examples both using +and not using `--verbose' to show the differences. + + Each instance of `--verbose' on the command line increases the +verbosity level by one, so if you need more details on the output, +specify it twice. + + When reading archives (`--list', `--extract', `--diff'), `tar' by +default prints only the names of the members being extracted. Using +`--verbose' will show a full, `ls' style member listing. + + In contrast, when writing archives (`--create', `--append', +`--update'), `tar' does not print file names by default. So, a single +`--verbose' option shows the file names being added to the archive, +while two `--verbose' options enable the full listing. + + For example, to create an archive in verbose mode: + + $ tar -cvf afiles.tar apple angst aspic + apple + angst + aspic + +Creating the same archive with the verbosity level 2 could give: + + $ tar -cvvf afiles.tar apple angst aspic + -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple + -rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst + -rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic + +This works equally well using short or long forms of options. Using +long forms, you would simply write out the mnemonic form of the option +twice, like this: + + $ tar --create --verbose --verbose ... + +Note that you must double the hyphens properly each time. + + Later in the tutorial, we will give examples using +`--verbose --verbose'. + + The full output consists of six fields: + + * File type and permissions in symbolic form. These are displayed + in the same format as the first column of `ls -l' output (*note + format=verbose: (fileutils)What information is listed.). + + * Owner name and group separated by a slash character. If these + data are not available (for example, when listing a `v7' format + archive), numeric ID values are printed instead. + + * Size of the file, in bytes. + + * File modification date in ISO 8601 format. + + * File modification time. + + * File name. If the name contains any special characters (white + space, newlines, etc.) these are displayed in an unambiguous form + using so called "quoting style". For the detailed discussion of + available styles and on how to use them, see *note quoting + styles::. + + Depending on the file type, the name can be followed by some + additional information, described in the following table: + + `-> LINK-NAME' + The file or archive member is a "symbolic link" and LINK-NAME + is the name of file it links to. + + `link to LINK-NAME' + The file or archive member is a "hard link" and LINK-NAME is + the name of file it links to. + + `--Long Link--' + The archive member is an old GNU format long link. You will + normally not encounter this. + + `--Long Name--' + The archive member is an old GNU format long name. You will + normally not encounter this. + + `--Volume Header--' + The archive member is a GNU "volume header" (*note Tape + Files::). + + `--Continued at byte N--' + Encountered only at the beginning of a multi-volume archive + (*note Using Multiple Tapes::). This archive member is a + continuation from the previous volume. The number N gives the + offset where the original file was split. + + `unknown file type C' + An archive member of unknown type. C is the type character + from the archive header. If you encounter such a message, it + means that either your archive contains proprietary member + types GNU `tar' is not able to handle, or the archive is + corrupted. + + + For example, here is an archive listing containing most of the +special suffixes explained above: + + V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header-- + -rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at + byte 32456-- + -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple + lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple + -rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues + hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues + + + +File: tar.info, Node: help tutorial, Prev: verbose tutorial, Up: Two Frequent Options + +Getting Help: Using the `--help' Option +--------------------------------------- + +`--help' + The `--help' option to `tar' prints out a very brief list of all + operations and option available for the current version of `tar' + available on your system. + + +File: tar.info, Node: create, Next: list, Prev: Two Frequent Options, Up: Tutorial + +2.6 How to Create Archives +========================== + + _(This message will disappear, once this node revised.)_ + +One of the basic operations of `tar' is `--create' (`-c'), which you +use to create a `tar' archive. We will explain `--create' first +because, in order to learn about the other operations, you will find it +useful to have an archive available to practice on. + + To make this easier, in this section you will first create a +directory containing three files. Then, we will show you how to create +an _archive_ (inside the new directory). Both the directory, and the +archive are specifically for you to practice on. The rest of this +chapter and the next chapter will show many examples using this +directory and the files you will create: some of those files may be +other directories and other archives. + + The three files you will archive in this example are called `blues', +`folk', and `jazz'. The archive is called `collection.tar'. + + This section will proceed slowly, detailing how to use `--create' in +`verbose' mode, and showing examples using both short and long forms. +In the rest of the tutorial, and in the examples in the next chapter, +we will proceed at a slightly quicker pace. This section moves more +slowly to allow beginning users to understand how `tar' works. + +* Menu: + +* prepare for examples:: +* Creating the archive:: +* create verbose:: +* short create:: +* create dir:: + + +File: tar.info, Node: prepare for examples, Next: Creating the archive, Up: create + +2.6.1 Preparing a Practice Directory for Examples +------------------------------------------------- + +To follow along with this and future examples, create a new directory +called `practice' containing files called `blues', `folk' and `jazz'. +The files can contain any information you like: ideally, they should +contain information which relates to their names, and be of different +lengths. Our examples assume that `practice' is a subdirectory of your +home directory. + + Now `cd' to the directory named `practice'; `practice' is now your +"working directory". (_Please note_: Although the full file name of +this directory is `/HOMEDIR/practice', in our examples we will refer to +this directory as `practice'; the HOMEDIR is presumed. + + In general, you should check that the files to be archived exist +where you think they do (in the working directory) by running `ls'. +Because you just created the directory and the files and have changed to +that directory, you probably don't need to do that this time. + + It is very important to make sure there isn't already a file in the +working directory with the archive name you intend to use (in this case, +`collection.tar'), or that you don't care about its contents. Whenever +you use `create', `tar' will erase the current contents of the file +named by `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') if it exists. `tar' +will not tell you if you are about to overwrite an archive unless you +specify an option which does this (*note backup::, for the information +on how to do so). To add files to an existing archive, you need to use +a different option, such as `--append' (`-r'); see *note append:: for +information on how to do this. + + +File: tar.info, Node: Creating the archive, Next: create verbose, Prev: prepare for examples, Up: create + +2.6.2 Creating the Archive +-------------------------- + +To place the files `blues', `folk', and `jazz' into an archive named +`collection.tar', use the following command: + + $ tar --create --file=collection.tar blues folk jazz + + The order of the arguments is not very important, _when using long +option forms_. You could also say: + + $ tar blues --create folk --file=collection.tar jazz + +However, you can see that this order is harder to understand; this is +why we will list the arguments in the order that makes the commands +easiest to understand (and we encourage you to do the same when you use +`tar', to avoid errors). + + Note that the sequence `--file=collection.tar' is considered to be +_one_ argument. If you substituted any other string of characters for +`collection.tar', then that string would become the name of the +archive file you create. + + The order of the options becomes more important when you begin to use +short forms. With short forms, if you type commands in the wrong order +(even if you type them correctly in all other ways), you may end up with +results you don't expect. For this reason, it is a good idea to get +into the habit of typing options in the order that makes inherent sense. +*Note short create::, for more information on this. + + In this example, you type the command as shown above: `--create' is +the operation which creates the new archive (`collection.tar'), and +`--file' is the option which lets you give it the name you chose. The +files, `blues', `folk', and `jazz', are now members of the archive, +`collection.tar' (they are "file name arguments" to the `--create' +operation. *Note Choosing::, for the detailed discussion on these.) +Now that they are in the archive, they are called _archive members_, +not files. (*note members: Definitions.). + + When you create an archive, you _must_ specify which files you want +placed in the archive. If you do not specify any archive members, GNU +`tar' will complain. + + If you now list the contents of the working directory (`ls'), you +will find the archive file listed as well as the files you saw +previously: + + blues folk jazz collection.tar + +Creating the archive `collection.tar' did not destroy the copies of the +files in the directory. + + Keep in mind that if you don't indicate an operation, `tar' will not +run and will prompt you for one. If you don't name any files, `tar' +will complain. You must have write access to the working directory, or +else you will not be able to create an archive in that directory. + + _Caution_: Do not attempt to use `--create' (`-c') to add files to +an existing archive; it will delete the archive and write a new one. +Use `--append' (`-r') instead. *Note append::. + + +File: tar.info, Node: create verbose, Next: short create, Prev: Creating the archive, Up: create + +2.6.3 Running `--create' with `--verbose' +----------------------------------------- + +If you include the `--verbose' (`-v') option on the command line, `tar' +will list the files it is acting on as it is working. In verbose mode, +the `create' example above would appear as: + + $ tar --create --verbose --file=collection.tar blues folk jazz + blues + folk + jazz + + This example is just like the example we showed which did not use +`--verbose', except that `tar' generated the remaining lines . + + In the rest of the examples in this chapter, we will frequently use +`verbose' mode so we can show actions or `tar' responses that you would +otherwise not see, and which are important for you to understand. + + +File: tar.info, Node: short create, Next: create dir, Prev: create verbose, Up: create + +2.6.4 Short Forms with `create' +------------------------------- + +As we said before, the `--create' (`-c') operation is one of the most +basic uses of `tar', and you will use it countless times. Eventually, +you will probably want to use abbreviated (or "short") forms of +options. A full discussion of the three different forms that options +can take appears in *note Styles::; for now, here is what the previous +example (including the `--verbose' (`-v') option) looks like using +short option forms: + + $ tar -cvf collection.tar blues folk jazz + blues + folk + jazz + +As you can see, the system responds the same no matter whether you use +long or short option forms. + + One difference between using short and long option forms is that, +although the exact placement of arguments following options is no more +specific when using short forms, it is easier to become confused and +make a mistake when using short forms. For example, suppose you +attempted the above example in the following way: + + $ tar -cfv collection.tar blues folk jazz + +In this case, `tar' will make an archive file called `v', containing +the files `blues', `folk', and `jazz', because the `v' is the closest +"file name" to the `-f' option, and is thus taken to be the chosen +archive file name. `tar' will try to add a file called +`collection.tar' to the `v' archive file; if the file `collection.tar' +did not already exist, `tar' will report an error indicating that this +file does not exist. If the file `collection.tar' does already exist +(e.g., from a previous command you may have run), then `tar' will add +this file to the archive. Because the `-v' option did not get +registered, `tar' will not run under `verbose' mode, and will not +report its progress. + + The end result is that you may be quite confused about what happened, +and possibly overwrite a file. To illustrate this further, we will show +you how an example we showed previously would look using short forms. + + This example, + + $ tar blues --create folk --file=collection.tar jazz + +is confusing as it is. When shown using short forms, however, it +becomes much more so: + + $ tar blues -c folk -f collection.tar jazz + +It would be very easy to put the wrong string of characters immediately +following the `-f', but doing that could sacrifice valuable data. + + For this reason, we recommend that you pay very careful attention to +the order of options and placement of file and archive names, +especially when using short option forms. Not having the option name +written out mnemonically can affect how well you remember which option +does what, and therefore where different names have to be placed. + + +File: tar.info, Node: create dir, Prev: short create, Up: create + +2.6.5 Archiving Directories +--------------------------- + +You can archive a directory by specifying its directory name as a file +name argument to `tar'. The files in the directory will be archived +relative to the working directory, and the directory will be re-created +along with its contents when the archive is extracted. + + To archive a directory, first move to its superior directory. If you +have followed the previous instructions in this tutorial, you should +type: + + $ cd .. + $ + +This will put you into the directory which contains `practice', i.e., +your home directory. Once in the superior directory, you can specify +the subdirectory, `practice', as a file name argument. To store +`practice' in the new archive file `music.tar', type: + + $ tar --create --verbose --file=music.tar practice + +`tar' should output: + + practice/ + practice/blues + practice/folk + practice/jazz + practice/collection.tar + + Note that the archive thus created is not in the subdirectory +`practice', but rather in the current working directory--the directory +from which `tar' was invoked. Before trying to archive a directory +from its superior directory, you should make sure you have write access +to the superior directory itself, not only the directory you are trying +archive with `tar'. For example, you will probably not be able to +store your home directory in an archive by invoking `tar' from the root +directory; *Note absolute::. (Note also that `collection.tar', the +original archive file, has itself been archived. `tar' will accept any +file as a file to be archived, regardless of its content. When +`music.tar' is extracted, the archive file `collection.tar' will be +re-written into the file system). + + If you give `tar' a command such as + + $ tar --create --file=foo.tar . + +`tar' will report `tar: ./foo.tar is the archive; not dumped'. This +happens because `tar' creates the archive `foo.tar' in the current +directory before putting any files into it. Then, when `tar' attempts +to add all the files in the directory `.' to the archive, it notices +that the file `./foo.tar' is the same as the archive `foo.tar', and +skips it. (It makes no sense to put an archive into itself.) GNU `tar' +will continue in this case, and create the archive normally, except for +the exclusion of that one file. (_Please note:_ Other implementations +of `tar' may not be so clever; they will enter an infinite loop when +this happens, so you should not depend on this behavior unless you are +certain you are running GNU `tar'. In general, it is wise to always +place the archive outside of the directory being dumped. + + +File: tar.info, Node: list, Next: extract, Prev: create, Up: Tutorial + +2.7 How to List Archives +======================== + +Frequently, you will find yourself wanting to determine exactly what a +particular archive contains. You can use the `--list' (`-t') operation +to get the member names as they currently appear in the archive, as +well as various attributes of the files at the time they were archived. +For example, you can examine the archive `collection.tar' that you +created in the last section with the command, + + $ tar --list --file=collection.tar + +The output of `tar' would then be: + + blues + folk + jazz + +The archive `bfiles.tar' would list as follows: + + ./birds + baboon + ./box + +Be sure to use a `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') option just +as with `--create' (`-c') to specify the name of the archive. + + If you use the `--verbose' (`-v') option with `--list', then `tar' +will print out a listing reminiscent of `ls -l', showing owner, file +size, and so forth. This output is described in detail in *note +verbose member listing::. + + If you had used `--verbose' (`-v') mode, the example above would +look like: + + $ tar --list --verbose --file=collection.tar folk + -rw-r--r-- myself user 62 1990-05-23 10:55 folk + + It is important to notice that the output of `tar --list --verbose' +does not necessarily match that produced by `tar --create --verbose' +while creating the archive. It is because GNU `tar', unless told +explicitly not to do so, removes some directory prefixes from file +names before storing them in the archive (*Note absolute::, for more +information). In other words, in verbose mode GNU `tar' shows "file +names" when creating an archive and "member names" when listing it. +Consider this example: + + $ tar cfv archive /etc/mail + tar: Removing leading `/' from member names + /etc/mail/ + /etc/mail/sendmail.cf + /etc/mail/aliases + $ tar tf archive + etc/mail/ + etc/mail/sendmail.cf + etc/mail/aliases + + This default behavior can sometimes be inconvenient. You can force +GNU `tar' show member names when creating archive by supplying +`--show-stored-names' option. + +`--show-stored-names' + Print member (as opposed to _file_) names when creating the + archive. + + You can specify one or more individual member names as arguments when +using `list'. In this case, `tar' will only list the names of members +you identify. For example, `tar --list --file=afiles.tar apple' would +only print `apple'. + + Because `tar' preserves file names, these must be specified as they +appear in the archive (i.e., relative to the directory from which the +archive was created). Therefore, it is essential when specifying +member names to `tar' that you give the exact member names. For +example, `tar --list --file=bfiles.tar birds' would produce an error +message something like `tar: birds: Not found in archive', because +there is no member named `birds', only one named `./birds'. While the +names `birds' and `./birds' name the same file, _member_ names by +default are compared verbatim. + + However, `tar --list --file=bfiles.tar baboon' would respond with +`baboon', because this exact member name is in the archive file +`bfiles.tar'. If you are not sure of the exact file name, use +"globbing patterns", for example: + + $ tar --list --file=bfiles.tar --wildcards '*b*' + +will list all members whose name contains `b'. *Note wildcards::, for +a detailed discussion of globbing patterns and related `tar' command +line options. + +* Menu: + +* list dir:: + + +File: tar.info, Node: list dir, Up: list + +Listing the Contents of a Stored Directory +------------------------------------------ + +To get information about the contents of an archived directory, use the +directory name as a file name argument in conjunction with `--list' +(`-t'). To find out file attributes, include the `--verbose' (`-v') +option. + + For example, to find out about files in the directory `practice', in +the archive file `music.tar', type: + + $ tar --list --verbose --file=music.tar practice + + `tar' responds: + + drwxrwxrwx myself user 0 1990-05-31 21:49 practice/ + -rw-r--r-- myself user 42 1990-05-21 13:29 practice/blues + -rw-r--r-- myself user 62 1990-05-23 10:55 practice/folk + -rw-r--r-- myself user 40 1990-05-21 13:30 practice/jazz + -rw-r--r-- myself user 10240 1990-05-31 21:49 practice/collection.tar + + When you use a directory name as a file name argument, `tar' acts on +all the files (including sub-directories) in that directory. + + +File: tar.info, Node: extract, Next: going further, Prev: list, Up: Tutorial + +2.8 How to Extract Members from an Archive +========================================== + + _(This message will disappear, once this node revised.)_ + +Creating an archive is only half the job--there is no point in storing +files in an archive if you can't retrieve them. The act of retrieving +members from an archive so they can be used and manipulated as +unarchived files again is called "extraction". To extract files from +an archive, use the `--extract' (`--get' or `-x') operation. As with +`--create', specify the name of the archive with `--file' (`-f') +option. Extracting an archive does not modify the archive in any way; +you can extract it multiple times if you want or need to. + + Using `--extract', you can extract an entire archive, or specific +files. The files can be directories containing other files, or not. As +with `--create' (`-c') and `--list' (`-t'), you may use the short or the +long form of the operation without affecting the performance. + +* Menu: + +* extracting archives:: +* extracting files:: +* extract dir:: +* extracting untrusted archives:: +* failing commands:: + + +File: tar.info, Node: extracting archives, Next: extracting files, Up: extract + +2.8.1 Extracting an Entire Archive +---------------------------------- + +To extract an entire archive, specify the archive file name only, with +no individual file names as arguments. For example, + + $ tar -xvf collection.tar + +produces this: + + -rw-r--r-- me user 28 1996-10-18 16:31 jazz + -rw-r--r-- me user 21 1996-09-23 16:44 blues + -rw-r--r-- me user 20 1996-09-23 16:44 folk + + +File: tar.info, Node: extracting files, Next: extract dir, Prev: extracting archives, Up: extract + +2.8.2 Extracting Specific Files +------------------------------- + +To extract specific archive members, give their exact member names as +arguments, as printed by `--list' (`-t'). If you had mistakenly +deleted one of the files you had placed in the archive `collection.tar' +earlier (say, `blues'), you can extract it from the archive without +changing the archive's structure. Its contents will be identical to +the original file `blues' that you deleted. + + First, make sure you are in the `practice' directory, and list the +files in the directory. Now, delete the file, `blues', and list the +files in the directory again. + + You can now extract the member `blues' from the archive file +`collection.tar' like this: + + $ tar --extract --file=collection.tar blues + +If you list the files in the directory again, you will see that the file +`blues' has been restored, with its original permissions, data +modification times, and owner.(1) (These parameters will be identical +to those which the file had when you originally placed it in the +archive; any changes you may have made before deleting the file from +the file system, however, will _not_ have been made to the archive +member.) The archive file, `collection.tar', is the same as it was +before you extracted `blues'. You can confirm this by running `tar' +with `--list' (`-t'). + + Remember that as with other operations, specifying the exact member +name is important. `tar --extract --file=bfiles.tar birds' will fail, +because there is no member named `birds'. To extract the member named +`./birds', you must specify `tar --extract --file=bfiles.tar ./birds'. +If you don't remember the exact member names, use `--list' (`-t') option +(*note list::). You can also extract those members that match a +specific "globbing pattern". For example, to extract from `bfiles.tar' +all files that begin with `b', no matter their directory prefix, you +could type: + + $ tar -x -f bfiles.tar --wildcards --no-anchored 'b*' + +Here, `--wildcards' instructs `tar' to treat command line arguments as +globbing patterns and `--no-anchored' informs it that the patterns +apply to member names after any `/' delimiter. The use of globbing +patterns is discussed in detail in *Note wildcards::. + + You can extract a file to standard output by combining the above +options with the `--to-stdout' (`-O') option (*note Writing to Standard +Output::). + + If you give the `--verbose' option, then `--extract' will print the +names of the archive members as it extracts them. + + ---------- Footnotes ---------- + + (1) This is only accidentally true, but not in general. Whereas +modification times are always restored, in most cases, one has to be +root for restoring the owner, and use a special option for restoring +permissions. Here, it just happens that the restoring user is also the +owner of the archived members, and that the current `umask' is +compatible with original permissions. + + +File: tar.info, Node: extract dir, Next: extracting untrusted archives, Prev: extracting files, Up: extract + +2.8.3 Extracting Files that are Directories +------------------------------------------- + +Extracting directories which are members of an archive is similar to +extracting other files. The main difference to be aware of is that if +the extracted directory has the same name as any directory already in +the working directory, then files in the extracted directory will be +placed into the directory of the same name. Likewise, if there are +files in the pre-existing directory with the same names as the members +which you extract, the files from the extracted archive will replace +the files already in the working directory (and possible +subdirectories). This will happen regardless of whether or not the +files in the working directory were more recent than those extracted +(there exist, however, special options that alter this behavior *note +Writing::). + + However, if a file was stored with a directory name as part of its +file name, and that directory does not exist under the working +directory when the file is extracted, `tar' will create the directory. + + We can demonstrate how to use `--extract' to extract a directory +file with an example. Change to the `practice' directory if you +weren't there, and remove the files `folk' and `jazz'. Then, go back +to the parent directory and extract the archive `music.tar'. You may +either extract the entire archive, or you may extract only the files +you just deleted. To extract the entire archive, don't give any file +names as arguments after the archive name `music.tar'. To extract only +the files you deleted, use the following command: + + $ tar -xvf music.tar practice/folk practice/jazz + practice/folk + practice/jazz + +If you were to specify two `--verbose' (`-v') options, `tar' would have +displayed more detail about the extracted files, as shown in the +example below: + + $ tar -xvvf music.tar practice/folk practice/jazz + -rw-r--r-- me user 28 1996-10-18 16:31 practice/jazz + -rw-r--r-- me user 20 1996-09-23 16:44 practice/folk + +Because you created the directory with `practice' as part of the file +names of each of the files by archiving the `practice' directory as +`practice', you must give `practice' as part of the file names when you +extract those files from the archive. + + +File: tar.info, Node: extracting untrusted archives, Next: failing commands, Prev: extract dir, Up: extract + +2.8.4 Extracting Archives from Untrusted Sources +------------------------------------------------ + +Extracting files from archives can overwrite files that already exist. +If you receive an archive from an untrusted source, you should make a +new directory and extract into that directory, so that you don't have +to worry about the extraction overwriting one of your existing files. +For example, if `untrusted.tar' came from somewhere else on the +Internet, and you don't necessarily trust its contents, you can extract +it as follows: + + $ mkdir newdir + $ cd newdir + $ tar -xvf ../untrusted.tar + + It is also a good practice to examine contents of the archive before +extracting it, using `--list' (`-t') option, possibly combined with +`--verbose' (`-v'). + + +File: tar.info, Node: failing commands, Prev: extracting untrusted archives, Up: extract + +2.8.5 Commands That Will Fail +----------------------------- + +Here are some sample commands you might try which will not work, and why +they won't work. + + If you try to use this command, + + $ tar -xvf music.tar folk jazz + +you will get the following response: + + tar: folk: Not found in archive + tar: jazz: Not found in archive + $ + +This is because these files were not originally _in_ the parent +directory `..', where the archive is located; they were in the +`practice' directory, and their file names reflect this: + + $ tar -tvf music.tar + practice/folk + practice/jazz + practice/rock + +Likewise, if you try to use this command, + + $ tar -tvf music.tar folk jazz + +you would get a similar response. Members with those names are not in +the archive. You must use the correct member names, or wildcards, in +order to extract the files from the archive. + + If you have forgotten the correct names of the files in the archive, +use `tar --list --verbose' to list them correctly. + + +File: tar.info, Node: going further, Prev: extract, Up: Tutorial + +2.9 Going Further Ahead in this Manual +====================================== + + +File: tar.info, Node: tar invocation, Next: operations, Prev: Tutorial, Up: Top + +3 Invoking GNU `tar' +******************** + + _(This message will disappear, once this node revised.)_ + +This chapter is about how one invokes the GNU `tar' command, from the +command synopsis (*note Synopsis::). There are numerous options, and +many styles for writing them. One mandatory option specifies the +operation `tar' should perform (*note Operation Summary::), other +options are meant to detail how this operation should be performed +(*note Option Summary::). Non-option arguments are not always +interpreted the same way, depending on what the operation is. + + You will find in this chapter everything about option styles and +rules for writing them (*note Styles::). On the other hand, operations +and options are fully described elsewhere, in other chapters. Here, +you will find only synthetic descriptions for operations and options, +together with pointers to other parts of the `tar' manual. + + Some options are so special they are fully described right in this +chapter. They have the effect of inhibiting the normal operation of +`tar' or else, they globally alter the amount of feedback the user +receives about what is going on. These are the `--help' and +`--version' (*note help::), `--verbose' (*note verbose::) and +`--interactive' options (*note interactive::). + +* Menu: + +* Synopsis:: +* using tar options:: +* Styles:: +* All Options:: +* help:: +* defaults:: +* verbose:: +* interactive:: + + +File: tar.info, Node: Synopsis, Next: using tar options, Up: tar invocation + +3.1 General Synopsis of `tar' +============================= + +The GNU `tar' program is invoked as either one of: + + tar OPTION... [NAME]... + tar LETTER... [ARGUMENT]... [OPTION]... [NAME]... + + The second form is for when old options are being used. + + You can use `tar' to store files in an archive, to extract them from +an archive, and to do other types of archive manipulation. The primary +argument to `tar', which is called the "operation", specifies which +action to take. The other arguments to `tar' are either "options", +which change the way `tar' performs an operation, or file names or +archive members, which specify the files or members `tar' is to act on. + + You can actually type in arguments in any order, even if in this +manual the options always precede the other arguments, to make examples +easier to understand. Further, the option stating the main operation +mode (the `tar' main command) is usually given first. + + Each NAME in the synopsis above is interpreted as an archive member +name when the main command is one of `--compare' (`--diff', `-d'), +`--delete', `--extract' (`--get', `-x'), `--list' (`-t') or `--update' +(`-u'). When naming archive members, you must give the exact name of +the member in the archive, as it is printed by `--list'. For +`--append' (`-r') and `--create' (`-c'), these NAME arguments specify +the names of either files or directory hierarchies to place in the +archive. These files or hierarchies should already exist in the file +system, prior to the execution of the `tar' command. + + `tar' interprets relative file names as being relative to the +working directory. `tar' will make all file names relative (by +removing leading slashes when archiving or restoring files), unless you +specify otherwise (using the `--absolute-names' option). *Note +absolute::, for more information about `--absolute-names'. + + If you give the name of a directory as either a file name or a member +name, then `tar' acts recursively on all the files and directories +beneath that directory. For example, the name `/' identifies all the +files in the file system to `tar'. + + The distinction between file names and archive member names is +especially important when shell globbing is used, and sometimes a +source of confusion for newcomers. *Note wildcards::, for more +information about globbing. The problem is that shells may only glob +using existing files in the file system. Only `tar' itself may glob on +archive members, so when needed, you must ensure that wildcard +characters reach `tar' without being interpreted by the shell first. +Using a backslash before `*' or `?', or putting the whole argument +between quotes, is usually sufficient for this. + + Even if NAMEs are often specified on the command line, they can also +be read from a text file in the file system, using the +`--files-from=FILE-OF-NAMES' (`-T FILE-OF-NAMES') option. + + If you don't use any file name arguments, `--append' (`-r'), +`--delete' and `--concatenate' (`--catenate', `-A') will do nothing, +while `--create' (`-c') will usually yield a diagnostic and inhibit +`tar' execution. The other operations of `tar' (`--list', `--extract', +`--compare', and `--update') will act on the entire contents of the +archive. + + Besides successful exits, GNU `tar' may fail for many reasons. Some +reasons correspond to bad usage, that is, when the `tar' command is +improperly written. Errors may be encountered later, while +encountering an error processing the archive or the files. Some errors +are recoverable, in which case the failure is delayed until `tar' has +completed all its work. Some errors are such that it would not +meaningful, or at least risky, to continue processing: `tar' then +aborts processing immediately. All abnormal exits, whether immediate +or delayed, should always be clearly diagnosed on `stderr', after a +line stating the nature of the error. + + Possible exit codes of GNU `tar' are summarized in the following +table: + +0 + `Successful termination'. + +1 + `Some files differ'. If tar was invoked with `--compare' + (`--diff', `-d') command line option, this means that some files + in the archive differ from their disk counterparts (*note + compare::). If tar was given `--create', `--append' or `--update' + option, this exit code means that some files were changed while + being archived and so the resulting archive does not contain the + exact copy of the file set. + +2 + `Fatal error'. This means that some fatal, unrecoverable error + occurred. + + If `tar' has invoked a subprocess and that subprocess exited with a +nonzero exit code, `tar' exits with that code as well. This can +happen, for example, if `tar' was given some compression option (*note +gzip::) and the external compressor program failed. Another example is +`rmt' failure during backup to the remote device (*note Remote Tape +Server::). + + +File: tar.info, Node: using tar options, Next: Styles, Prev: Synopsis, Up: tar invocation + +3.2 Using `tar' Options +======================= + +GNU `tar' has a total of eight operating modes which allow you to +perform a variety of tasks. You are required to choose one operating +mode each time you employ the `tar' program by specifying one, and only +one operation as an argument to the `tar' command (two lists of four +operations each may be found at *note frequent operations:: and *note +Operations::). Depending on circumstances, you may also wish to +customize how the chosen operating mode behaves. For example, you may +wish to change the way the output looks, or the format of the files +that you wish to archive may require you to do something special in +order to make the archive look right. + + You can customize and control `tar''s performance by running `tar' +with one or more options (such as `--verbose' (`-v'), which we used in +the tutorial). As we said in the tutorial, "options" are arguments to +`tar' which are (as their name suggests) optional. Depending on the +operating mode, you may specify one or more options. Different options +will have different effects, but in general they all change details of +the operation, such as archive format, archive name, or level of user +interaction. Some options make sense with all operating modes, while +others are meaningful only with particular modes. You will likely use +some options frequently, while you will only use others infrequently, or +not at all. (A full list of options is available in *note All +Options::.) + + The `TAR_OPTIONS' environment variable specifies default options to +be placed in front of any explicit options. For example, if +`TAR_OPTIONS' is `-v --unlink-first', `tar' behaves as if the two +options `-v' and `--unlink-first' had been specified before any +explicit options. Option specifications are separated by whitespace. +A backslash escapes the next character, so it can be used to specify an +option containing whitespace or a backslash. + + Note that `tar' options are case sensitive. For example, the +options `-T' and `-t' are different; the first requires an argument for +stating the name of a file providing a list of NAMEs, while the second +does not require an argument and is another way to write `--list' +(`-t'). + + In addition to the eight operations, there are many options to +`tar', and three different styles for writing both: long (mnemonic) +form, short form, and old style. These styles are discussed below. +Both the options and the operations can be written in any of these three +styles. + + +File: tar.info, Node: Styles, Next: All Options, Prev: using tar options, Up: tar invocation + +3.3 The Three Option Styles +=========================== + +There are three styles for writing operations and options to the command +line invoking `tar'. The different styles were developed at different +times during the history of `tar'. These styles will be presented +below, from the most recent to the oldest. + + Some options must take an argument. (For example, `--file' (`-f')) +takes the name of an archive file as an argument. If you do not supply +an archive file name, `tar' will use a default, but this can be +confusing; thus, we recommend that you always supply a specific archive +file name.) Where you _place_ the arguments generally depends on which +style of options you choose. We will detail specific information +relevant to each option style in the sections on the different option +styles, below. The differences are subtle, yet can often be very +important; incorrect option placement can cause you to overwrite a +number of important files. We urge you to note these differences, and +only use the option style(s) which makes the most sense to you until +you feel comfortable with the others. + + Some options _may_ take an argument. Such options may have at most +long and short forms, they do not have old style equivalent. The rules +for specifying an argument for such options are stricter than those for +specifying mandatory arguments. Please, pay special attention to them. + +* Menu: + +* Long Options:: Long Option Style +* Short Options:: Short Option Style +* Old Options:: Old Option Style +* Mixing:: Mixing Option Styles + + +File: tar.info, Node: Long Options, Next: Short Options, Up: Styles + +3.3.1 Long Option Style +----------------------- + +Each option has at least one "long" (or "mnemonic") name starting with +two dashes in a row, e.g., `--list'. The long names are more clear than +their corresponding short or old names. It sometimes happens that a +single long option has many different names which are synonymous, such +as `--compare' and `--diff'. In addition, long option names can be +given unique abbreviations. For example, `--cre' can be used in place +of `--create' because there is no other long option which begins with +`cre'. (One way to find this out is by trying it and seeing what +happens; if a particular abbreviation could represent more than one +option, `tar' will tell you that that abbreviation is ambiguous and +you'll know that that abbreviation won't work. You may also choose to +run `tar --help' to see a list of options. Be aware that if you run +`tar' with a unique abbreviation for the long name of an option you +didn't want to use, you are stuck; `tar' will perform the command as +ordered.) + + Long options are meant to be obvious and easy to remember, and their +meanings are generally easier to discern than those of their +corresponding short options (see below). For example: + + $ tar --create --verbose --blocking-factor=20 --file=/dev/rmt0 + +gives a fairly good set of hints about what the command does, even for +those not fully acquainted with `tar'. + + Long options which require arguments take those arguments +immediately following the option name. There are two ways of +specifying a mandatory argument. It can be separated from the option +name either by an equal sign, or by any amount of white space +characters. For example, the `--file' option (which tells the name of +the `tar' archive) is given a file such as `archive.tar' as argument by +using any of the following notations: `--file=archive.tar' or `--file +archive.tar'. + + In contrast, optional arguments must always be introduced using an +equal sign. For example, the `--backup' option takes an optional +argument specifying backup type. It must be used as +`--backup=BACKUP-TYPE'. + + +File: tar.info, Node: Short Options, Next: Old Options, Prev: Long Options, Up: Styles + +3.3.2 Short Option Style +------------------------ + +Most options also have a "short option" name. Short options start with +a single dash, and are followed by a single character, e.g., `-t' +(which is equivalent to `--list'). The forms are absolutely identical +in function; they are interchangeable. + + The short option names are faster to type than long option names. + + Short options which require arguments take their arguments +immediately following the option, usually separated by white space. It +is also possible to stick the argument right after the short option +name, using no intervening space. For example, you might write +`-f archive.tar' or `-farchive.tar' instead of using +`--file=archive.tar'. Both `--file=ARCHIVE-NAME' and `-f ARCHIVE-NAME' +denote the option which indicates a specific archive, here named +`archive.tar'. + + Short options which take optional arguments take their arguments +immediately following the option letter, _without any intervening white +space characters_. + + Short options' letters may be clumped together, but you are not +required to do this (as compared to old options; see below). When +short options are clumped as a set, use one (single) dash for them all, +e.g., ``tar' -cvf'. Only the last option in such a set is allowed to +have an argument(1). + + When the options are separated, the argument for each option which +requires an argument directly follows that option, as is usual for Unix +programs. For example: + + $ tar -c -v -b 20 -f /dev/rmt0 + + If you reorder short options' locations, be sure to move any +arguments that belong to them. If you do not move the arguments +properly, you may end up overwriting files. + + ---------- Footnotes ---------- + + (1) Clustering many options, the last of which has an argument, is a +rather opaque way to write options. Some wonder if GNU `getopt' should +not even be made helpful enough for considering such usages as invalid. + + +File: tar.info, Node: Old Options, Next: Mixing, Prev: Short Options, Up: Styles + +3.3.3 Old Option Style +---------------------- + + _(This message will disappear, once this node revised.)_ + +Like short options, "old options" are single letters. However, old +options must be written together as a single clumped set, without +spaces separating them or dashes preceding them(1). This set of +letters must be the first to appear on the command line, after the +`tar' program name and some white space; old options cannot appear +anywhere else. The letter of an old option is exactly the same letter +as the corresponding short option. For example, the old option `t' is +the same as the short option `-t', and consequently, the same as the +long option `--list'. So for example, the command `tar cv' specifies +the option `-v' in addition to the operation `-c'. + + When options that need arguments are given together with the command, +all the associated arguments follow, in the same order as the options. +Thus, the example given previously could also be written in the old +style as follows: + + $ tar cvbf 20 /dev/rmt0 + +Here, `20' is the argument of `-b' and `/dev/rmt0' is the argument of +`-f'. + + On the other hand, this old style syntax makes it difficult to match +option letters with their corresponding arguments, and is often +confusing. In the command `tar cvbf 20 /dev/rmt0', for example, `20' +is the argument for `-b', `/dev/rmt0' is the argument for `-f', and +`-v' does not have a corresponding argument. Even using short options +like in `tar -c -v -b 20 -f /dev/rmt0' is clearer, putting all +arguments next to the option they pertain to. + + If you want to reorder the letters in the old option argument, be +sure to reorder any corresponding argument appropriately. + + This old way of writing `tar' options can surprise even experienced +users. For example, the two commands: + + tar cfz archive.tar.gz file + tar -cfz archive.tar.gz file + +are quite different. The first example uses `archive.tar.gz' as the +value for option `f' and recognizes the option `z'. The second +example, however, uses `z' as the value for option `f' -- probably not +what was intended. + + Old options are kept for compatibility with old versions of `tar'. + + This second example could be corrected in many ways, among which the +following are equivalent: + + tar -czf archive.tar.gz file + tar -cf archive.tar.gz -z file + tar cf archive.tar.gz -z file + + As far as we know, all `tar' programs, GNU and non-GNU, support old +options. GNU `tar' supports them not only for historical reasons, but +also because many people are used to them. For compatibility with Unix +`tar', the first argument is always treated as containing command and +option letters even if it doesn't start with `-'. Thus, `tar c' is +equivalent to `tar -c': both of them specify the `--create' (`-c') +command to create an archive. + + ---------- Footnotes ---------- + + (1) Beware that if you precede options with a dash, you are +announcing the short option style instead of the old option style; +short options are decoded differently. + + +File: tar.info, Node: Mixing, Prev: Old Options, Up: Styles + +3.3.4 Mixing Option Styles +-------------------------- + +All three styles may be intermixed in a single `tar' command, so long +as the rules for each style are fully respected(1). Old style options +and either of the modern styles of options may be mixed within a single +`tar' command. However, old style options must be introduced as the +first arguments only, following the rule for old options (old options +must appear directly after the `tar' command and some white space). +Modern options may be given only after all arguments to the old options +have been collected. If this rule is not respected, a modern option +might be falsely interpreted as the value of the argument to one of the +old style options. + + For example, all the following commands are wholly equivalent, and +illustrate the many combinations and orderings of option styles. + + tar --create --file=archive.tar + tar --create -f archive.tar + tar --create -farchive.tar + tar --file=archive.tar --create + tar --file=archive.tar -c + tar -c --file=archive.tar + tar -c -f archive.tar + tar -c -farchive.tar + tar -cf archive.tar + tar -cfarchive.tar + tar -f archive.tar --create + tar -f archive.tar -c + tar -farchive.tar --create + tar -farchive.tar -c + tar c --file=archive.tar + tar c -f archive.tar + tar c -farchive.tar + tar cf archive.tar + tar f archive.tar --create + tar f archive.tar -c + tar fc archive.tar + + On the other hand, the following commands are _not_ equivalent to +the previous set: + + tar -f -c archive.tar + tar -fc archive.tar + tar -fcarchive.tar + tar -farchive.tarc + tar cfarchive.tar + +These last examples mean something completely different from what the +user intended (judging based on the example in the previous set which +uses long options, whose intent is therefore very clear). The first +four specify that the `tar' archive would be a file named `-c', `c', +`carchive.tar' or `archive.tarc', respectively. The first two examples +also specify a single non-option, NAME argument having the value +`archive.tar'. The last example contains only old style option letters +(repeating option `c' twice), not all of which are meaningful (eg., `.', +`h', or `i'), with no argument value. + + ---------- Footnotes ---------- + + (1) Before GNU `tar' version 1.11.6, a bug prevented intermixing old +style options with long options in some cases. + + +File: tar.info, Node: All Options, Next: help, Prev: Styles, Up: tar invocation + +3.4 All `tar' Options +===================== + +The coming manual sections contain an alphabetical listing of all `tar' +operations and options, with brief descriptions and cross references to +more in-depth explanations in the body of the manual. They also +contain an alphabetically arranged table of the short option forms with +their corresponding long option. You can use this table as a reference +for deciphering `tar' commands in scripts. + +* Menu: + +* Operation Summary:: +* Option Summary:: +* Short Option Summary:: + + +File: tar.info, Node: Operation Summary, Next: Option Summary, Up: All Options + +3.4.1 Operations +---------------- + +`--append' +`-r' + Appends files to the end of the archive. *Note append::. + +`--catenate' +`-A' + Same as `--concatenate'. *Note concatenate::. + +`--compare' +`-d' + Compares archive members with their counterparts in the file + system, and reports differences in file size, mode, owner, + modification date and contents. *Note compare::. + +`--concatenate' +`-A' + Appends other `tar' archives to the end of the archive. *Note + concatenate::. + +`--create' +`-c' + Creates a new `tar' archive. *Note create::. + +`--delete' + Deletes members from the archive. Don't try this on a archive on a + tape! *Note delete::. + +`--diff' +`-d' + Same `--compare'. *Note compare::. + +`--extract' +`-x' + Extracts members from the archive into the file system. *Note + extract::. + +`--get' +`-x' + Same as `--extract'. *Note extract::. + +`--list' +`-t' + Lists the members in an archive. *Note list::. + +`--update' +`-u' + Adds files to the end of the archive, but only if they are newer + than their counterparts already in the archive, or if they do not + already exist in the archive. *Note update::. + + + +File: tar.info, Node: Option Summary, Next: Short Option Summary, Prev: Operation Summary, Up: All Options + +3.4.2 `tar' Options +------------------- + +`--absolute-names' +`-P' + Normally when creating an archive, `tar' strips an initial `/' + from member names. This option disables that behavior. *Note + absolute::. + +`--after-date' + (See `--newer', *note after::) + +`--anchored' + A pattern must match an initial subsequence of the name's + components. *Note controlling pattern-matching::. + +`--atime-preserve' +`--atime-preserve=replace' +`--atime-preserve=system' + Attempt to preserve the access time of files when reading them. + This option currently is effective only on files that you own, + unless you have superuser privileges. + + `--atime-preserve=replace' remembers the access time of a file + before reading it, and then restores the access time afterwards. + This may cause problems if other programs are reading the file at + the same time, as the times of their accesses will be lost. On + most platforms restoring the access time also requires `tar' to + restore the data modification time too, so this option may also + cause problems if other programs are writing the file at the same + time. (Tar attempts to detect this situation, but cannot do so + reliably due to race conditions.) Worse, on most platforms + restoring the access time also updates the status change time, + which means that this option is incompatible with incremental + backups. + + `--atime-preserve=system' avoids changing time stamps on files, + without interfering with time stamp updates caused by other + programs, so it works better with incremental backups. However, + it requires a special `O_NOATIME' option from the underlying + operating and file system implementation, and it also requires + that searching directories does not update their access times. As + of this writing (November 2005) this works only with Linux, and + only with Linux kernels 2.6.8 and later. Worse, there is + currently no reliable way to know whether this feature actually + works. Sometimes `tar' knows that it does not work, and if you use + `--atime-preserve=system' then `tar' complains and exits right + away. But other times `tar' might think that the option works + when it actually does not. + + Currently `--atime-preserve' with no operand defaults to + `--atime-preserve=replace', but this may change in the future as + support for `--atime-preserve=system' improves. + + If your operating system does not support + `--atime-preserve=system', you might be able to preserve access + times reliably by by using the `mount' command. For example, you + can mount the file system read-only, or access the file system via + a read-only loopback mount, or use the `noatime' mount option + available on some systems. However, mounting typically requires + superuser privileges and can be a pain to manage. + +`--backup=BACKUP-TYPE' + Rather than deleting files from the file system, `tar' will back + them up using simple or numbered backups, depending upon + BACKUP-TYPE. *Note backup::. + +`--block-number' +`-R' + With this option present, `tar' prints error messages for read + errors with the block number in the archive file. *Note + block-number::. + +`--blocking-factor=BLOCKING' +`-b BLOCKING' + Sets the blocking factor `tar' uses to BLOCKING x 512 bytes per + record. *Note Blocking Factor::. + +`--bzip2' +`-j' + This option tells `tar' to read or write archives through `bzip2'. + *Note gzip::. + +`--checkpoint[=NUMBER]' + This option directs `tar' to print periodic checkpoint messages as + it reads through the archive. It is intended for when you want a + visual indication that `tar' is still running, but don't want to + see `--verbose' output. For a detailed description, see *note + Progress information::. + +`--check-links' +`-l' + If this option was given, `tar' will check the number of links + dumped for each processed file. If this number does not match the + total number of hard links for the file, a warning message will be + output (1). + +`--compress' +`--uncompress' +`-Z' + `tar' will use the `compress' program when reading or writing the + archive. This allows you to directly act on archives while saving + space. *Note gzip::. + +`--confirmation' + (See `--interactive'.) *Note interactive::. + +`--delay-directory-restore' + Delay setting modification times and permissions of extracted + directories until the end of extraction. *Note Directory + Modification Times and Permissions::. + +`--dereference' +`-h' + When creating a `tar' archive, `tar' will archive the file that a + symbolic link points to, rather than archiving the symlink. *Note + dereference::. + +`--directory=DIR' +`-C DIR' + When this option is specified, `tar' will change its current + directory to DIR before performing any operations. When this + option is used during archive creation, it is order sensitive. + *Note directory::. + +`--exclude=PATTERN' + When performing operations, `tar' will skip files that match + PATTERN. *Note exclude::. + +`--exclude-from=FILE' +`-X FILE' + Similar to `--exclude', except `tar' will use the list of patterns + in the file FILE. *Note exclude::. + +`--exclude-caches' + Exclude from dump any directory containing a valid cache directory + tag file, but still dump the directory node and the tag file + itself. + + *Note exclude::. + +`--exclude-caches-under' + Exclude from dump any directory containing a valid cache directory + tag file, but still dump the directory node itself. + + *Note exclude::. + +`--exclude-caches-all' + Exclude from dump any directory containing a valid cache directory + tag file. *Note exclude::. + +`--exclude-tag=FILE' + Exclude from dump any directory containing file named FILE, but + dump the directory node and FILE itself. *Note exclude::. + +`--exclude-tag-under=FILE' + Exclude from dump the contents of any directory containing file + named FILE, but dump the directory node itself. *Note exclude::. + +`--exclude-tag-all=FILE' + Exclude from dump any directory containing file named FILE. *Note + exclude::. + +`--file=ARCHIVE' +`-f ARCHIVE' + `tar' will use the file ARCHIVE as the `tar' archive it performs + operations on, rather than `tar''s compilation dependent default. + *Note file tutorial::. + +`--files-from=FILE' +`-T FILE' + `tar' will use the contents of FILE as a list of archive members + or files to operate on, in addition to those specified on the + command-line. *Note files::. + +`--force-local' + Forces `tar' to interpret the file name given to `--file' as a + local file, even if it looks like a remote tape drive name. *Note + local and remote archives::. + +`--format=FORMAT' +`-H FORMAT' + Selects output archive format. FORMAT may be one of the following: + + `v7' + Creates an archive that is compatible with Unix V7 `tar'. + + `oldgnu' + Creates an archive that is compatible with GNU `tar' version + 1.12 or earlier. + + `gnu' + Creates archive in GNU tar 1.13 format. Basically it is the + same as `oldgnu' with the only difference in the way it + handles long numeric fields. + + `ustar' + Creates a POSIX.1-1988 compatible archive. + + `posix' + Creates a POSIX.1-2001 archive. + + + *Note Formats::, for a detailed discussion of these formats. + +`--group=GROUP' + Files added to the `tar' archive will have a group ID of GROUP, + rather than the group from the source file. GROUP is first decoded + as a group symbolic name, but if this interpretation fails, it has + to be a decimal numeric group ID. *Note override::. + + Also see the comments for the `--owner=USER' option. + +`--gzip' +`--gunzip' +`--ungzip' +`-z' + This option tells `tar' to read or write archives through `gzip', + allowing `tar' to directly operate on several kinds of compressed + archives transparently. *Note gzip::. + +`--help' +`-?' + `tar' will print out a short message summarizing the operations and + options to `tar' and exit. *Note help::. + +`--ignore-case' + Ignore case when matching member or file names with patterns. + *Note controlling pattern-matching::. + +`--ignore-command-error' + Ignore exit codes of subprocesses. *Note Writing to an External + Program::. + +`--ignore-failed-read' + Do not exit unsuccessfully merely because an unreadable file was + encountered. *Note Reading::. + +`--ignore-zeros' +`-i' + With this option, `tar' will ignore zeroed blocks in the archive, + which normally signals EOF. *Note Reading::. + +`--incremental' +`-G' + Informs `tar' that it is working with an old GNU-format + incremental backup archive. It is intended primarily for + backwards compatibility only. *Note Incremental Dumps::, for a + detailed discussion of incremental archives. + +`--index-file=FILE' + Send verbose output to FILE instead of to standard output. + +`--info-script=SCRIPT-FILE' +`--new-volume-script=SCRIPT-FILE' +`-F SCRIPT-FILE' + When `tar' is performing multi-tape backups, SCRIPT-FILE is run at + the end of each tape. If SCRIPT-FILE exits with nonzero status, + `tar' fails immediately. *Note info-script::, for a detailed + discussion of SCRIPT-FILE. + +`--interactive' +`--confirmation' +`-w' + Specifies that `tar' should ask the user for confirmation before + performing potentially destructive options, such as overwriting + files. *Note interactive::. + +`--keep-newer-files' + Do not replace existing files that are newer than their archive + copies when extracting files from an archive. + +`--keep-old-files' +`-k' + Do not overwrite existing files when extracting files from an + archive. *Note Keep Old Files::. + +`--label=NAME' +`-V NAME' + When creating an archive, instructs `tar' to write NAME as a name + record in the archive. When extracting or listing archives, `tar' + will only operate on archives that have a label matching the + pattern specified in NAME. *Note Tape Files::. + +`--listed-incremental=SNAPSHOT-FILE' +`-g SNAPSHOT-FILE' + During a `--create' operation, specifies that the archive that + `tar' creates is a new GNU-format incremental backup, using + SNAPSHOT-FILE to determine which files to backup. With other + operations, informs `tar' that the archive is in incremental + format. *Note Incremental Dumps::. + +`--mode=PERMISSIONS' + When adding files to an archive, `tar' will use PERMISSIONS for + the archive members, rather than the permissions from the files. + PERMISSIONS can be specified either as an octal number or as + symbolic permissions, like with `chmod'. *Note override::. + +`--mtime=DATE' + When adding files to an archive, `tar' will use DATE as the + modification time of members when creating archives, instead of + their actual modification times. The value of DATE can be either + a textual date representation (*note Date input formats::) or a + name of the existing file, starting with `/' or `.'. In the + latter case, the modification time of that file is used. *Note + override::. + +`--multi-volume' +`-M' + Informs `tar' that it should create or otherwise operate on a + multi-volume `tar' archive. *Note Using Multiple Tapes::. + +`--new-volume-script' + (see -info-script) + +`--newer=DATE' +`--after-date=DATE' +`-N' + When creating an archive, `tar' will only add files that have + changed since DATE. If DATE begins with `/' or `.', it is taken + to be the name of a file whose data modification time specifies + the date. *Note after::. + +`--newer-mtime=DATE' + Like `--newer', but add only files whose contents have changed (as + opposed to just `--newer', which will also back up files for which + any status information has changed). *Note after::. + +`--no-anchored' + An exclude pattern can match any subsequence of the name's + components. *Note controlling pattern-matching::. + +`--no-delay-directory-restore' + Modification times and permissions of extracted directories are + set when all files from this directory have been extracted. This + is the default. *Note Directory Modification Times and + Permissions::. + +`--no-ignore-case' + Use case-sensitive matching. *Note controlling pattern-matching::. + +`--no-ignore-command-error' + Print warnings about subprocesses that terminated with a nonzero + exit code. *Note Writing to an External Program::. + +`--no-overwrite-dir' + Preserve metadata of existing directories when extracting files + from an archive. *Note Overwrite Old Files::. + +`--no-quote-chars=STRING' + Remove characters listed in STRING from the list of quoted + characters set by the previous `--quote-chars' option (*note + quoting styles::). + +`--no-recursion' + With this option, `tar' will not recurse into directories. *Note + recurse::. + +`--no-same-owner' +`-o' + When extracting an archive, do not attempt to preserve the owner + specified in the `tar' archive. This the default behavior for + ordinary users. + +`--no-same-permissions' + When extracting an archive, subtract the user's umask from files + from the permissions specified in the archive. This is the + default behavior for ordinary users. + +`--no-unquote' + Treat all input file or member names literally, do not interpret + escape sequences. *Note input name quoting::. + +`--no-wildcards' + Do not use wildcards. *Note controlling pattern-matching::. + +`--no-wildcards-match-slash' + Wildcards do not match `/'. *Note controlling pattern-matching::. + +`--null' + When `tar' is using the `--files-from' option, this option + instructs `tar' to expect file names terminated with NUL, so `tar' + can correctly work with file names that contain newlines. *Note + nul::. + +`--numeric-owner' + This option will notify `tar' that it should use numeric user and + group IDs when creating a `tar' file, rather than names. *Note + Attributes::. + +`-o' + The function of this option depends on the action `tar' is + performing. When extracting files, `-o' is a synonym for + `--no-same-owner', i.e., it prevents `tar' from restoring + ownership of files being extracted. + + When creating an archive, it is a synonym for `--old-archive'. + This behavior is for compatibility with previous versions of GNU + `tar', and will be removed in future releases. + + *Note Changes::, for more information. + +`--occurrence[=NUMBER]' + This option can be used in conjunction with one of the subcommands + `--delete', `--diff', `--extract' or `--list' when a list of files + is given either on the command line or via `-T' option. + + This option instructs `tar' to process only the NUMBERth + occurrence of each named file. NUMBER defaults to 1, so + + tar -x -f archive.tar --occurrence filename + + will extract the first occurrence of the member `filename' from + `archive.tar' and will terminate without scanning to the end of + the archive. + +`--old-archive' + Synonym for `--format=v7'. + +`--one-file-system' + Used when creating an archive. Prevents `tar' from recursing into + directories that are on different file systems from the current + directory (2). + +`--overwrite' + Overwrite existing files and directory metadata when extracting + files from an archive. *Note Overwrite Old Files::. + +`--overwrite-dir' + Overwrite the metadata of existing directories when extracting + files from an archive. *Note Overwrite Old Files::. + +`--owner=USER' + Specifies that `tar' should use USER as the owner of members when + creating archives, instead of the user associated with the source + file. USER is first decoded as a user symbolic name, but if this + interpretation fails, it has to be a decimal numeric user ID. + *Note override::. + + This option does not affect extraction from archives. + +`--pax-option=KEYWORD-LIST' + This option is meaningful only with POSIX.1-2001 archives (*note + posix::). It modifies the way `tar' handles the extended header + keywords. KEYWORD-LIST is a comma-separated list of keyword + options. *Note PAX keywords::, for a detailed discussion. + +`--portability' +`--old-archive' + Synonym for `--format=v7'. + +`--posix' + Same as `--format=posix'. + +`--preserve' + Synonymous with specifying both `--preserve-permissions' and + `--same-order'. *Note Setting Access Permissions::. + +`--preserve-order' + (See `--same-order'; *note Reading::.) + +`--preserve-permissions' +`--same-permissions' +`-p' + When `tar' is extracting an archive, it normally subtracts the + users' umask from the permissions specified in the archive and uses + that number as the permissions to create the destination file. + Specifying this option instructs `tar' that it should use the + permissions directly from the archive. *Note Setting Access + Permissions::. + +`--quote-chars=STRING' + Always quote characters from STRING, even if the selected quoting + style would not quote them (*note quoting styles::). + +`--quoting-style=STYLE' + Set quoting style to use when printing member and file names + (*note quoting styles::). Valid STYLE values are: `literal', + `shell', `shell-always', `c', `escape', `locale', and `clocale'. + Default quoting style is `escape', unless overridden while + configuring the package. + +`--read-full-records' +`-B' + Specifies that `tar' should reblock its input, for reading from + pipes on systems with buggy implementations. *Note Reading::. + +`--record-size=SIZE' + Instructs `tar' to use SIZE bytes per record when accessing the + archive. *Note Blocking Factor::. + +`--recursion' + With this option, `tar' recurses into directories (default). + *Note recurse::. + +`--recursive-unlink' + Remove existing directory hierarchies before extracting + directories of the same name from the archive. *Note Recursive + Unlink::. + +`--remove-files' + Directs `tar' to remove the source file from the file system after + appending it to an archive. *Note remove files::. + +`--restrict' + Disable use of some potentially harmful `tar' options. Currently + this option disables shell invocation from multi-volume menu + (*note Using Multiple Tapes::). + +`--rmt-command=CMD' + Notifies `tar' that it should use CMD instead of the default + `/usr/libexec/rmt' (*note Remote Tape Server::). + +`--rsh-command=CMD' + Notifies `tar' that is should use CMD to communicate with remote + devices. *Note Device::. + +`--same-order' +`--preserve-order' +`-s' + This option is an optimization for `tar' when running on machines + with small amounts of memory. It informs `tar' that the list of + file arguments has already been sorted to match the order of files + in the archive. *Note Reading::. + +`--same-owner' + When extracting an archive, `tar' will attempt to preserve the + owner specified in the `tar' archive with this option present. + This is the default behavior for the superuser; this option has an + effect only for ordinary users. *Note Attributes::. + +`--same-permissions' + (See `--preserve-permissions'; *note Setting Access Permissions::.) + +`--seek' +`-n' + Assume that the archive media supports seeks to arbitrary + locations. Usually `tar' determines automatically whether the + archive can be seeked or not. This option is intended for use in + cases when such recognition fails. + +`--show-defaults' + Displays the default options used by `tar' and exits successfully. + This option is intended for use in shell scripts. Here is an + example of what you can see using this option: + + $ tar --show-defaults + --format=gnu -f- -b20 --quoting-style=escape \ + --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh + +`--show-omitted-dirs' + Instructs `tar' to mention the directories it is skipping when + operating on a `tar' archive. *Note show-omitted-dirs::. + +`--show-transformed-names' +`--show-stored-names' + Display file or member names after applying any transformations + (*note transform::). In particular, when used in conjunction with + one of the archive creation operations it instructs `tar' to list + the member names stored in the archive, as opposed to the actual + file names. *Note listing member and file names::. + +`--sparse' +`-S' + Invokes a GNU extension when adding files to an archive that + handles sparse files efficiently. *Note sparse::. + +`--sparse-version=VERSION' + Specifies the "format version" to use when archiving sparse files. + Implies `--sparse'. *Note sparse::. For the description of the + supported sparse formats, *Note Sparse Formats::. + +`--starting-file=NAME' +`-K NAME' + This option affects extraction only; `tar' will skip extracting + files in the archive until it finds one that matches NAME. *Note + Scarce::. + +`--strip-components=NUMBER' + Strip given NUMBER of leading components from file names before + extraction. For example, if archive `archive.tar' contained + `/some/file/name', then running + + tar --extract --file archive.tar --strip-components=2 + + would extract this file to file `name'. + + , summary + +`--suffix=SUFFIX' + Alters the suffix `tar' uses when backing up files from the default + `~'. *Note backup::. + +`--tape-length=NUM' +`-L NUM' + Specifies the length of tapes that `tar' is writing as being + NUM x 1024 bytes long. *Note Using Multiple Tapes::. + +`--test-label' + Reads the volume label. If an argument is specified, test whether + it matches the volume label. *Note --test-label option::. + +`--to-command=COMMAND' + During extraction `tar' will pipe extracted files to the standard + input of COMMAND. *Note Writing to an External Program::. + +`--to-stdout' +`-O' + During extraction, `tar' will extract files to stdout rather than + to the file system. *Note Writing to Standard Output::. + +`--totals[=SIGNO]' + Displays the total number of bytes transferred when processing an + archive. If an argument is given, these data are displayed on + request, when signal SIGNO is delivered to `tar'. *Note totals::. + +`--touch' +`-m' + Sets the data modification time of extracted files to the + extraction time, rather than the data modification time stored in + the archive. *Note Data Modification Times::. + +`--transform=SED-EXPR' + Transform file or member names using `sed' replacement expression + SED-EXPR. For example, + + $ tar cf archive.tar --transform 's,^\./,usr/,' . + + will add to `archive' files from the current working directory, + replacing initial `./' prefix with `usr/'. For the detailed + discussion, *Note transform::. + + To see transformed member names in verbose listings, use + `--show-transformed-names' option (*note show-transformed-names::). + +`--uncompress' + (See `--compress'. *note gzip::) + +`--ungzip' + (See `--gzip'. *note gzip::) + +`--unlink-first' +`-U' + Directs `tar' to remove the corresponding file from the file + system before extracting it from the archive. *Note Unlink + First::. + +`--unquote' + Enable unquoting input file or member names (default). *Note + input name quoting::. + +`--use-compress-program=PROG' + Instructs `tar' to access the archive through PROG, which is + presumed to be a compression program of some sort. *Note gzip::. + +`--utc' + Display file modification dates in UTC. This option implies + `--verbose'. + +`--verbose' +`-v' + Specifies that `tar' should be more verbose about the operations + it is performing. This option can be specified multiple times for + some operations to increase the amount of information displayed. + *Note verbose::. + +`--verify' +`-W' + Verifies that the archive was correctly written when creating an + archive. *Note verify::. + +`--version' + Print information about the program's name, version, origin and + legal status, all on standard output, and then exit successfully. + *Note help::. + +`--volno-file=FILE' + Used in conjunction with `--multi-volume'. `tar' will keep track + of which volume of a multi-volume archive it is working in FILE. + *Note volno-file::. + +`--wildcards' + Use wildcards when matching member names with patterns. *Note + controlling pattern-matching::. + +`--wildcards-match-slash' + Wildcards match `/'. *Note controlling pattern-matching::. + + ---------- Footnotes ---------- + + (1) Earlier versions of GNU `tar' understood `-l' as a synonym for +`--one-file-system'. The current semantics, which complies to UNIX98, +was introduced with version 1.15.91. *Note Changes::, for more +information. + + (2) Earlier versions of GNU `tar' understood `-l' as a synonym for +`--one-file-system'. This has changed in version 1.15.91. *Note +Changes::, for more information. + + +File: tar.info, Node: Short Option Summary, Prev: Option Summary, Up: All Options + +3.4.3 Short Options Cross Reference +----------------------------------- + +Here is an alphabetized list of all of the short option forms, matching +them with the equivalent long option. + +Short Option Reference +-------------------------------------------------------------------------- +-A *note --concatenate::. +-B *note --read-full-records::. +-C *note --directory::. +-F *note --info-script::. +-G *note --incremental::. +-K *note --starting-file::. +-L *note --tape-length::. +-M *note --multi-volume::. +-N *note --newer::. +-O *note --to-stdout::. +-P *note --absolute-names::. +-R *note --block-number::. +-S *note --sparse::. +-T *note --files-from::. +-U *note --unlink-first::. +-V *note --label::. +-W *note --verify::. +-X *note --exclude-from::. +-Z *note --compress::. +-b *note --blocking-factor::. +-c *note --create::. +-d *note --compare::. +-f *note --file::. +-g *note --listed-incremental::. +-h *note --dereference::. +-i *note --ignore-zeros::. +-j *note --bzip2::. +-k *note --keep-old-files::. +-l *note --check-links::. +-m *note --touch::. +-o When creating, *note --no-same-owner::, when extracting -- + *note --portability::. + + The later usage is deprecated. It is retained for + compatibility with the earlier versions of GNU `tar'. In + future releases `-o' will be equivalent to + `--no-same-owner' only. +-p *note --preserve-permissions::. +-r *note --append::. +-s *note --same-order::. +-t *note --list::. +-u *note --update::. +-v *note --verbose::. +-w *note --interactive::. +-x *note --extract::. +-z *note --gzip::. + + +File: tar.info, Node: help, Next: defaults, Prev: All Options, Up: tar invocation + +3.5 GNU `tar' documentation +=========================== + +Being careful, the first thing is really checking that you are using +GNU `tar', indeed. The `--version' option causes `tar' to print +information about its name, version, origin and legal status, all on +standard output, and then exit successfully. For example, +`tar --version' might print: + + tar (GNU tar) 1.17 + Copyright (C) 2006 Free Software Foundation, Inc. + This is free software. You may redistribute copies of it under the terms + of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>. + There is NO WARRANTY, to the extent permitted by law. + + Written by John Gilmore and Jay Fenlason. + +The first occurrence of `tar' in the result above is the program name +in the package (for example, `rmt' is another program), while the +second occurrence of `tar' is the name of the package itself, +containing possibly many programs. The package is currently named +`tar', after the name of the main program it contains(1). + + Another thing you might want to do is checking the spelling or +meaning of some particular `tar' option, without resorting to this +manual, for once you have carefully read it. GNU `tar' has a short +help feature, triggerable through the `--help' option. By using this +option, `tar' will print a usage message listing all available options +on standard output, then exit successfully, without doing anything else +and ignoring all other options. Even if this is only a brief summary, +it may be several screens long. So, if you are not using some kind of +scrollable window, you might prefer to use something like: + + $ tar --help | less + +presuming, here, that you like using `less' for a pager. Other popular +pagers are `more' and `pg'. If you know about some KEYWORD which +interests you and do not want to read all the `--help' output, another +common idiom is doing: + + tar --help | grep KEYWORD + +for getting only the pertinent lines. Notice, however, that some `tar' +options have long description lines and the above command will list +only the first of them. + + The exact look of the option summary displayed by `tar --help' is +configurable. *Note Configuring Help Summary::, for a detailed +description. + + If you only wish to check the spelling of an option, running `tar +--usage' may be a better choice. This will display a terse list of +`tar' option without accompanying explanations. + + The short help output is quite succinct, and you might have to get +back to the full documentation for precise points. If you are reading +this paragraph, you already have the `tar' manual in some form. This +manual is available in a variety of forms from +`http://www.gnu.org/software/tar/manual'. It may be printed out of the +GNU `tar' distribution, provided you have TeX already installed +somewhere, and a laser printer around. Just configure the +distribution, execute the command `make dvi', then print `doc/tar.dvi' +the usual way (contact your local guru to know how). If GNU `tar' has +been conveniently installed at your place, this manual is also +available in interactive, hypertextual form as an Info file. Just call +`info tar' or, if you do not have the `info' program handy, use the +Info reader provided within GNU Emacs, calling `tar' from the main Info +menu. + + There is currently no `man' page for GNU `tar'. If you observe such +a `man' page on the system you are running, either it does not belong +to GNU `tar', or it has not been produced by GNU. Some package +maintainers convert `tar --help' output to a man page, using +`help2man'. In any case, please bear in mind that the authoritative +source of information about GNU `tar' is this Texinfo documentation. + + ---------- Footnotes ---------- + + (1) There are plans to merge the `cpio' and `tar' packages into a +single one which would be called `paxutils'. So, who knows if, one of +this days, the `--version' would not output `tar (GNU paxutils) 3.2' + + +File: tar.info, Node: defaults, Next: verbose, Prev: help, Up: tar invocation + +3.6 Obtaining GNU `tar' default values +====================================== + +GNU `tar' has some predefined defaults that are used when you do not +explicitly specify another values. To obtain a list of such defaults, +use `--show-defaults' option. This will output the values in the form +of `tar' command line options: + + tar --show-defaults + --format=gnu -f- -b20 --quoting-style=escape + --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh + +Notice, that this option outputs only one line. The example output +above has been split to fit page boundaries. + +The above output shows that this version of GNU `tar' defaults to using +`gnu' archive format (*note Formats::), it uses standard output as the +archive, if no `--file' option has been given (*note file tutorial::), +the default blocking factor is 20 (*note Blocking Factor::). It also +shows the default locations where `tar' will look for `rmt' and `rsh' +binaries. + + +File: tar.info, Node: verbose, Next: interactive, Prev: defaults, Up: tar invocation + +3.7 Checking `tar' progress +=========================== + +Typically, `tar' performs most operations without reporting any +information to the user except error messages. When using `tar' with +many options, particularly ones with complicated or +difficult-to-predict behavior, it is possible to make serious mistakes. +`tar' provides several options that make observing `tar' easier. These +options cause `tar' to print information as it progresses in its job, +and you might want to use them just for being more careful about what +is going on, or merely for entertaining yourself. If you have +encountered a problem when operating on an archive, however, you may +need more information than just an error message in order to solve the +problem. The following options can be helpful diagnostic tools. + + Normally, the `--list' (`-t') command to list an archive prints just +the file names (one per line) and the other commands are silent. When +used with most operations, the `--verbose' (`-v') option causes `tar' +to print the name of each file or archive member as it is processed. +This and the other options which make `tar' print status information +can be useful in monitoring `tar'. + + With `--create' or `--extract', `--verbose' used once just prints +the names of the files or members as they are processed. Using it +twice causes `tar' to print a longer listing (*Note verbose member +listing::, for the description) for each member. Since `--list' +already prints the names of the members, `--verbose' used once with +`--list' causes `tar' to print an `ls -l' type listing of the files in +the archive. The following examples both extract members with long +list output: + + $ tar --extract --file=archive.tar --verbose --verbose + $ tar xvvf archive.tar + + Verbose output appears on the standard output except when an archive +is being written to the standard output, as with `tar --create --file=- +--verbose' (`tar cfv -', or even `tar cv'--if the installer let +standard output be the default archive). In that case `tar' writes +verbose output to the standard error stream. + + If `--index-file=FILE' is specified, `tar' sends verbose output to +FILE rather than to standard output or standard error. + + The `--totals' option causes `tar' to print on the standard error +the total amount of bytes transferred when processing an archive. When +creating or appending to an archive, this option prints the number of +bytes written to the archive and the average speed at which they have +been written, e.g.: + + $ tar -c -f archive.tar --totals /home + Total bytes written: 7924664320 (7.4GiB, 85MiB/s) + + When reading an archive, this option displays the number of bytes +read: + + $ tar -x -f archive.tar --totals + Total bytes read: 7924664320 (7.4GiB, 95MiB/s) + + Finally, when deleting from an archive, the `--totals' option +displays both numbers plus number of bytes removed from the archive: + + $ tar --delete -f foo.tar --totals --wildcards '*~' + Total bytes read: 9543680 (9.2MiB, 201MiB/s) + Total bytes written: 3829760 (3.7MiB, 81MiB/s) + Total bytes deleted: 1474048 + + You can also obtain this information on request. When `--totals' is +used with an argument, this argument is interpreted as a symbolic name +of a signal, upon delivery of which the statistics is to be printed: + +`--totals=SIGNO' + Print statistics upon delivery of signal SIGNO. Valid arguments + are: `SIGHUP', `SIGQUIT', `SIGINT', `SIGUSR1' and `SIGUSR2'. + Shortened names without `SIG' prefix are also accepted. + + Both forms of `--totals' option can be used simultaneously. Thus, +`tar -x --totals --totals=USR1' instructs `tar' to extract all members +from its default archive and print statistics after finishing the +extraction, as well as when receiving signal `SIGUSR1'. + + The `--checkpoint' option prints an occasional message as `tar' +reads or writes the archive. It is designed for those who don't need +the more detailed (and voluminous) output of `--block-number' (`-R'), +but do want visual confirmation that `tar' is actually making forward +progress. By default it prints a message each 10 records read or +written. This can be changed by giving it a numeric argument after an +equal sign: + + $ tar -c --checkpoint=1000 /var + tar: Write checkpoint 1000 + tar: Write checkpoint 2000 + tar: Write checkpoint 3000 + + This example shows the default checkpoint message used by `tar'. If +you place a dot immediately after the equal sign, it will print a `.' +at each checkpoint. For example: + + $ tar -c --checkpoint=.1000 /var + ... + + The `--show-omitted-dirs' option, when reading an archive--with +`--list' or `--extract', for example--causes a message to be printed +for each directory in the archive which is skipped. This happens +regardless of the reason for skipping: the directory might not have +been named on the command line (implicitly or explicitly), it might be +excluded by the use of the `--exclude=PATTERN' option, or some other +reason. + + If `--block-number' (`-R') is used, `tar' prints, along with every +message it would normally produce, the block number within the archive +where the message was triggered. Also, supplementary messages are +triggered when reading blocks full of NULs, or when hitting end of file +on the archive. As of now, if the archive if properly terminated with +a NUL block, the reading of the file may stop before end of file is +met, so the position of end of file will not usually show when +`--block-number' (`-R') is used. Note that GNU `tar' drains the +archive before exiting when reading the archive from a pipe. + + This option is especially useful when reading damaged archives, since +it helps pinpoint the damaged sections. It can also be used with +`--list' (`-t') when listing a file-system backup tape, allowing you to +choose among several backup tapes when retrieving a file later, in +favor of the tape where the file appears earliest (closest to the front +of the tape). *Note backup::. + + +File: tar.info, Node: interactive, Prev: verbose, Up: tar invocation + +3.8 Asking for Confirmation During Operations +============================================= + +Typically, `tar' carries out a command without stopping for further +instructions. In some situations however, you may want to exclude some +files and archive members from the operation (for instance if disk or +storage space is tight). You can do this by excluding certain files +automatically (*note Choosing::), or by performing an operation +interactively, using the `--interactive' (`-w') option. `tar' also +accepts `--confirmation' for this option. + + When the `--interactive' (`-w') option is specified, before reading, +writing, or deleting files, `tar' first prints a message for each such +file, telling what operation it intends to take, then asks for +confirmation on the terminal. The actions which require confirmation +include adding a file to the archive, extracting a file from the +archive, deleting a file from the archive, and deleting a file from +disk. To confirm the action, you must type a line of input beginning +with `y'. If your input line begins with anything other than `y', +`tar' skips that file. + + If `tar' is reading the archive from the standard input, `tar' opens +the file `/dev/tty' to support the interactive communications. + + Verbose output is normally sent to standard output, separate from +other error messages. However, if the archive is produced directly on +standard output, then verbose output is mixed with errors on `stderr'. +Producing the archive on standard output may be used as a way to avoid +using disk space, when the archive is soon to be consumed by another +process reading it, say. Some people felt the need of producing an +archive on stdout, still willing to segregate between verbose output +and error output. A possible approach would be using a named pipe to +receive the archive, and having the consumer process to read from that +named pipe. This has the advantage of letting standard output free to +receive verbose output, all separate from errors. + + +File: tar.info, Node: operations, Next: Backups, Prev: tar invocation, Up: Top + +4 GNU `tar' Operations +********************** + +* Menu: + +* Basic tar:: +* Advanced tar:: +* create options:: +* extract options:: +* backup:: +* Applications:: +* looking ahead:: + + +File: tar.info, Node: Basic tar, Next: Advanced tar, Up: operations + +4.1 Basic GNU `tar' Operations +============================== + +The basic `tar' operations, `--create' (`-c'), `--list' (`-t') and +`--extract' (`--get', `-x'), are currently presented and described in +the tutorial chapter of this manual. This section provides some +complementary notes for these operations. + +`--create' +`-c' + Creating an empty archive would have some kind of elegance. One + can initialize an empty archive and later use `--append' (`-r') + for adding all members. Some applications would not welcome + making an exception in the way of adding the first archive member. + On the other hand, many people reported that it is dangerously + too easy for `tar' to destroy a magnetic tape with an empty + archive(1). The two most common errors are: + + 1. Mistakingly using `create' instead of `extract', when the + intent was to extract the full contents of an archive. This + error is likely: keys `c' and `x' are right next to each + other on the QWERTY keyboard. Instead of being unpacked, the + archive then gets wholly destroyed. When users speak about + "exploding" an archive, they usually mean something else :-). + + 2. Forgetting the argument to `file', when the intent was to + create an archive with a single file in it. This error is + likely because a tired user can easily add the `f' key to the + cluster of option letters, by the mere force of habit, + without realizing the full consequence of doing so. The + usual consequence is that the single file, which was meant to + be saved, is rather destroyed. + + So, recognizing the likelihood and the catastrophic nature of these + errors, GNU `tar' now takes some distance from elegance, and + cowardly refuses to create an archive when `--create' option is + given, there are no arguments besides options, and `--files-from' + (`-T') option is _not_ used. To get around the cautiousness of + GNU `tar' and nevertheless create an archive with nothing in it, + one may still use, as the value for the `--files-from' option, a + file with no names in it, as shown in the following commands: + + tar --create --file=empty-archive.tar --files-from=/dev/null + tar cfT empty-archive.tar /dev/null + +`--extract' +`--get' +`-x' + A socket is stored, within a GNU `tar' archive, as a pipe. + +``--list' (`-t')' + GNU `tar' now shows dates as `1996-08-30', while it used to show + them as `Aug 30 1996'. Preferably, people should get used to ISO + 8601 dates. Local American dates should be made available again + with full date localization support, once ready. In the meantime, + programs not being localizable for dates should prefer + international dates, that's really the way to go. + + Look up `http://www.cl.cam.ac.uk/~mgk25/iso-time.html' if you are + curious, it contains a detailed explanation of the ISO 8601 + standard. + + + ---------- Footnotes ---------- + + (1) This is well described in `Unix-haters Handbook', by Simson +Garfinkel, Daniel Weise & Steven Strassmann, IDG Books, ISBN +1-56884-203-1. + + +File: tar.info, Node: Advanced tar, Next: create options, Prev: Basic tar, Up: operations + +4.2 Advanced GNU `tar' Operations +================================= + +Now that you have learned the basics of using GNU `tar', you may want +to learn about further ways in which `tar' can help you. + + This chapter presents five, more advanced operations which you +probably won't use on a daily basis, but which serve more specialized +functions. We also explain the different styles of options and why you +might want to use one or another, or a combination of them in your `tar' +commands. Additionally, this chapter includes options which allow you +to define the output from `tar' more carefully, and provide help and +error correction in special circumstances. + +* Menu: + +* Operations:: +* append:: +* update:: +* concatenate:: +* delete:: +* compare:: + + +File: tar.info, Node: Operations, Next: append, Up: Advanced tar + +4.2.1 The Five Advanced `tar' Operations +---------------------------------------- + + _(This message will disappear, once this node revised.)_ + +In the last chapter, you learned about the first three operations to +`tar'. This chapter presents the remaining five operations to `tar': +`--append', `--update', `--concatenate', `--delete', and `--compare'. + + You are not likely to use these operations as frequently as those +covered in the last chapter; however, since they perform specialized +functions, they are quite useful when you do need to use them. We will +give examples using the same directory and files that you created in +the last chapter. As you may recall, the directory is called +`practice', the files are `jazz', `blues', `folk', `rock', and the two +archive files you created are `collection.tar' and `music.tar'. + + We will also use the archive files `afiles.tar' and `bfiles.tar'. +The archive `afiles.tar' contains the members `apple', `angst', and +`aspic'; `bfiles.tar' contains the members `./birds', `baboon', and +`./box'. + + Unless we state otherwise, all practicing you do and examples you +follow in this chapter will take place in the `practice' directory that +you created in the previous chapter; see *note prepare for examples::. +(Below in this section, we will remind you of the state of the examples +where the last chapter left them.) + + The five operations that we will cover in this chapter are: + +`--append' +`-r' + Add new entries to an archive that already exists. + +`--update' +`-r' + Add more recent copies of archive members to the end of an + archive, if they exist. + +`--concatenate' +`--catenate' +`-A' + Add one or more pre-existing archives to the end of another + archive. + +`--delete' + Delete items from an archive (does not work on tapes). + +`--compare' +`--diff' +`-d' + Compare archive members to their counterparts in the file system. + + +File: tar.info, Node: append, Next: update, Prev: Operations, Up: Advanced tar + +4.2.2 How to Add Files to Existing Archives: `--append' +------------------------------------------------------- + + _(This message will disappear, once this node revised.)_ + +If you want to add files to an existing archive, you don't need to +create a new archive; you can use `--append' (`-r'). The archive must +already exist in order to use `--append'. (A related operation is the +`--update' operation; you can use this to add newer versions of archive +members to an existing archive. To learn how to do this with +`--update', *note update::.) + + If you use `--append' to add a file that has the same name as an +archive member to an archive containing that archive member, then the +old member is not deleted. What does happen, however, is somewhat +complex. `tar' _allows_ you to have infinite number of files with the +same name. Some operations treat these same-named members no +differently than any other set of archive members: for example, if you +view an archive with `--list' (`-t'), you will see all of those members +listed, with their data modification times, owners, etc. + + Other operations don't deal with these members as perfectly as you +might prefer; if you were to use `--extract' to extract the archive, +only the most recently added copy of a member with the same name as four +other members would end up in the working directory. This is because +`--extract' extracts an archive in the order the members appeared in +the archive; the most recently archived members will be extracted last. +Additionally, an extracted member will _replace_ a file of the same +name which existed in the directory already, and `tar' will not prompt +you about this(1). Thus, only the most recently archived member will +end up being extracted, as it will replace the one extracted before it, +and so on. + + There exists a special option that allows you to get around this +behavior and extract (or list) only a particular copy of the file. +This is `--occurrence' option. If you run `tar' with this option, it +will extract only the first copy of the file. You may also give this +option an argument specifying the number of copy to be extracted. +Thus, for example if the archive `archive.tar' contained three copies +of file `myfile', then the command + + tar --extract --file archive.tar --occurrence=2 myfile + +would extract only the second copy. *Note --occurrence: Option +Summary, for the description of `--occurrence' option. + + If you want to replace an archive member, use `--delete' to delete +the member you want to remove from the archive, , and then use +`--append' to add the member you want to be in the archive. Note that +you can not change the order of the archive; the most recently added +member will still appear last. In this sense, you cannot truly +"replace" one member with another. (Replacing one member with another +will not work on certain types of media, such as tapes; see *note +delete:: and *note Media::, for more information.) + +* Menu: + +* appending files:: Appending Files to an Archive +* multiple:: + + ---------- Footnotes ---------- + + (1) Unless you give it `--keep-old-files' option, or the disk copy +is newer than the the one in the archive and you invoke `tar' with +`--keep-newer-files' option + + +File: tar.info, Node: appending files, Next: multiple, Up: append + +4.2.2.1 Appending Files to an Archive +..................................... + + _(This message will disappear, once this node revised.)_ + +The simplest way to add a file to an already existing archive is the +`--append' (`-r') operation, which writes specified files into the +archive whether or not they are already among the archived files. + + When you use `--append', you _must_ specify file name arguments, as +there is no default. If you specify a file that already exists in the +archive, another copy of the file will be added to the end of the +archive. As with other operations, the member names of the newly added +files will be exactly the same as their names given on the command +line. The `--verbose' (`-v') option will print out the names of the +files as they are written into the archive. + + `--append' cannot be performed on some tape drives, unfortunately, +due to deficiencies in the formats those tape drives use. The archive +must be a valid `tar' archive, or else the results of using this +operation will be unpredictable. *Note Media::. + + To demonstrate using `--append' to add a file to an archive, create +a file called `rock' in the `practice' directory. Make sure you are in +the `practice' directory. Then, run the following `tar' command to add +`rock' to `collection.tar': + + $ tar --append --file=collection.tar rock + +If you now use the `--list' (`-t') operation, you will see that `rock' +has been added to the archive: + + $ tar --list --file=collection.tar + -rw-r--r-- me user 28 1996-10-18 16:31 jazz + -rw-r--r-- me user 21 1996-09-23 16:44 blues + -rw-r--r-- me user 20 1996-09-23 16:44 folk + -rw-r--r-- me user 20 1996-09-23 16:44 rock + + +File: tar.info, Node: multiple, Prev: appending files, Up: append + +4.2.2.2 Multiple Members with the Same Name +........................................... + +You can use `--append' (`-r') to add copies of files which have been +updated since the archive was created. (However, we do not recommend +doing this since there is another `tar' option called `--update'; *Note +update::, for more information. We describe this use of `--append' +here for the sake of completeness.) When you extract the archive, the +older version will be effectively lost. This works because files are +extracted from an archive in the order in which they were archived. +Thus, when the archive is extracted, a file archived later in time will +replace a file of the same name which was archived earlier, even though +the older version of the file will remain in the archive unless you +delete all versions of the file. + + Supposing you change the file `blues' and then append the changed +version to `collection.tar'. As you saw above, the original `blues' is +in the archive `collection.tar'. If you change the file and append the +new version of the file to the archive, there will be two copies in the +archive. When you extract the archive, the older version of the file +will be extracted first, and then replaced by the newer version when it +is extracted. + + You can append the new, changed copy of the file `blues' to the +archive in this way: + + $ tar --append --verbose --file=collection.tar blues + blues + +Because you specified the `--verbose' option, `tar' has printed the +name of the file being appended as it was acted on. Now list the +contents of the archive: + + $ tar --list --verbose --file=collection.tar + -rw-r--r-- me user 28 1996-10-18 16:31 jazz + -rw-r--r-- me user 21 1996-09-23 16:44 blues + -rw-r--r-- me user 20 1996-09-23 16:44 folk + -rw-r--r-- me user 20 1996-09-23 16:44 rock + -rw-r--r-- me user 58 1996-10-24 18:30 blues + +The newest version of `blues' is now at the end of the archive (note +the different creation dates and file sizes). If you extract the +archive, the older version of the file `blues' will be replaced by the +newer version. You can confirm this by extracting the archive and +running `ls' on the directory. + + If you wish to extract the first occurrence of the file `blues' from +the archive, use `--occurrence' option, as shown in the following +example: + + $ tar --extract -vv --occurrence --file=collection.tar blues + -rw-r--r-- me user 21 1996-09-23 16:44 blues + + *Note Writing::, for more information on `--extract' and *Note +-occurrence: Option Summary, for the description of `--occurrence' +option. + + +File: tar.info, Node: update, Next: concatenate, Prev: append, Up: Advanced tar + +4.2.3 Updating an Archive +------------------------- + + _(This message will disappear, once this node revised.)_ + +In the previous section, you learned how to use `--append' to add a +file to an existing archive. A related operation is `--update' (`-u'). +The `--update' operation updates a `tar' archive by comparing the date +of the specified archive members against the date of the file with the +same name. If the file has been modified more recently than the +archive member, then the newer version of the file is added to the +archive (as with `--append'). + + Unfortunately, you cannot use `--update' with magnetic tape drives. +The operation will fail. + + Both `--update' and `--append' work by adding to the end of the +archive. When you extract a file from the archive, only the version +stored last will wind up in the file system, unless you use the +`--backup' option. *Note multiple::, for a detailed discussion. + +* Menu: + +* how to update:: + + +File: tar.info, Node: how to update, Up: update + +4.2.3.1 How to Update an Archive Using `--update' +................................................. + +You must use file name arguments with the `--update' (`-u') operation. +If you don't specify any files, `tar' won't act on any files and won't +tell you that it didn't do anything (which may end up confusing you). + + To see the `--update' option at work, create a new file, +`classical', in your practice directory, and some extra text to the +file `blues', using any text editor. Then invoke `tar' with the +`update' operation and the `--verbose' (`-v') option specified, using +the names of all the files in the practice directory as file name +arguments: + + $ tar --update -v -f collection.tar blues folk rock classical + blues + classical + $ + +Because we have specified verbose mode, `tar' prints out the names of +the files it is working on, which in this case are the names of the +files that needed to be updated. If you run `tar --list' and look at +the archive, you will see `blues' and `classical' at its end. There +will be a total of two versions of the member `blues'; the one at the +end will be newer and larger, since you added text before updating it. + + (The reason `tar' does not overwrite the older file when updating it +is because writing to the middle of a section of tape is a difficult +process. Tapes are not designed to go backward. *Note Media::, for +more information about tapes. + + `--update' (`-u') is not suitable for performing backups for two +reasons: it does not change directory content entries, and it lengthens +the archive every time it is used. The GNU `tar' options intended +specifically for backups are more efficient. If you need to run +backups, please consult *note Backups::. + + +File: tar.info, Node: concatenate, Next: delete, Prev: update, Up: Advanced tar + +4.2.4 Combining Archives with `--concatenate' +--------------------------------------------- + +Sometimes it may be convenient to add a second archive onto the end of +an archive rather than adding individual files to the archive. To add +one or more archives to the end of another archive, you should use the +`--concatenate' (`--catenate', `-A') operation. + + To use `--concatenate', give the first archive with `--file' option +and name the rest of archives to be concatenated on the command line. +The members, and their member names, will be copied verbatim from those +archives to the first one. (1) The new, concatenated archive will be +called by the same name as the one given with the `--file' option. As +usual, if you omit `--file', `tar' will use the value of the environment +variable `TAPE', or, if this has not been set, the default archive name. + + To demonstrate how `--concatenate' works, create two small archives +called `bluesrock.tar' and `folkjazz.tar', using the relevant files +from `practice': + + $ tar -cvf bluesrock.tar blues rock + blues + rock + $ tar -cvf folkjazz.tar folk jazz + folk + jazz + +If you like, You can run `tar --list' to make sure the archives contain +what they are supposed to: + + $ tar -tvf bluesrock.tar + -rw-r--r-- melissa user 105 1997-01-21 19:42 blues + -rw-r--r-- melissa user 33 1997-01-20 15:34 rock + $ tar -tvf jazzfolk.tar + -rw-r--r-- melissa user 20 1996-09-23 16:44 folk + -rw-r--r-- melissa user 65 1997-01-30 14:15 jazz + + We can concatenate these two archives with `tar': + + $ cd .. + $ tar --concatenate --file=bluesrock.tar jazzfolk.tar + + If you now list the contents of the `bluesrock.tar', you will see +that now it also contains the archive members of `jazzfolk.tar': + + $ tar --list --file=bluesrock.tar + blues + rock + folk + jazz + + When you use `--concatenate', the source and target archives must +already exist and must have been created using compatible format +parameters. Notice, that `tar' does not check whether the archives it +concatenates have compatible formats, it does not even check if the +files are really tar archives. + + Like `--append' (`-r'), this operation cannot be performed on some +tape drives, due to deficiencies in the formats those tape drives use. + + It may seem more intuitive to you to want or try to use `cat' to +concatenate two archives instead of using the `--concatenate' +operation; after all, `cat' is the utility for combining files. + + However, `tar' archives incorporate an end-of-file marker which must +be removed if the concatenated archives are to be read properly as one +archive. `--concatenate' removes the end-of-archive marker from the +target archive before each new archive is appended. If you use `cat' +to combine the archives, the result will not be a valid `tar' format +archive. If you need to retrieve files from an archive that was added +to using the `cat' utility, use the `--ignore-zeros' (`-i') option. +*Note Ignore Zeros::, for further information on dealing with archives +improperly combined using the `cat' shell utility. + + ---------- Footnotes ---------- + + (1) This can cause multiple members to have the same name, for +information on how this affects reading the archive, *note multiple::. + + +File: tar.info, Node: delete, Next: compare, Prev: concatenate, Up: Advanced tar + +4.2.5 Removing Archive Members Using `--delete' +----------------------------------------------- + + _(This message will disappear, once this node revised.)_ + +You can remove members from an archive by using the `--delete' option. +Specify the name of the archive with `--file' (`-f') and then specify +the names of the members to be deleted; if you list no member names, +nothing will be deleted. The `--verbose' option will cause `tar' to +print the names of the members as they are deleted. As with +`--extract', you must give the exact member names when using `tar +--delete'. `--delete' will remove all versions of the named file from +the archive. The `--delete' operation can run very slowly. + + Unlike other operations, `--delete' has no short form. + + This operation will rewrite the archive. You can only use +`--delete' on an archive if the archive device allows you to write to +any point on the media, such as a disk; because of this, it does not +work on magnetic tapes. Do not try to delete an archive member from a +magnetic tape; the action will not succeed, and you will be likely to +scramble the archive and damage your tape. There is no safe way +(except by completely re-writing the archive) to delete files from most +kinds of magnetic tape. *Note Media::. + + To delete all versions of the file `blues' from the archive +`collection.tar' in the `practice' directory, make sure you are in that +directory, and then, + + $ tar --list --file=collection.tar + blues + folk + jazz + rock + $ tar --delete --file=collection.tar blues + $ tar --list --file=collection.tar + folk + jazz + rock + $ + + The `--delete' option has been reported to work properly when `tar' +acts as a filter from `stdin' to `stdout'. + + +File: tar.info, Node: compare, Prev: delete, Up: Advanced tar + +4.2.6 Comparing Archive Members with the File System +---------------------------------------------------- + + _(This message will disappear, once this node revised.)_ + +The `--compare' (`-d'), or `--diff' operation compares specified +archive members against files with the same names, and then reports +differences in file size, mode, owner, modification date and contents. +You should _only_ specify archive member names, not file names. If you +do not name any members, then `tar' will compare the entire archive. +If a file is represented in the archive but does not exist in the file +system, `tar' reports a difference. + + You have to specify the record size of the archive when modifying an +archive with a non-default record size. + + `tar' ignores files in the file system that do not have +corresponding members in the archive. + + The following example compares the archive members `rock', `blues' +and `funk' in the archive `bluesrock.tar' with files of the same name +in the file system. (Note that there is no file, `funk'; `tar' will +report an error message.) + + $ tar --compare --file=bluesrock.tar rock blues funk + rock + blues + tar: funk not found in archive + + The spirit behind the `--compare' (`--diff', `-d') option is to +check whether the archive represents the current state of files on +disk, more than validating the integrity of the archive media. For +this later goal, *Note verify::. + + +File: tar.info, Node: create options, Next: extract options, Prev: Advanced tar, Up: operations + +4.3 Options Used by `--create' +============================== + +The previous chapter described the basics of how to use `--create' +(`-c') to create an archive from a set of files. *Note create::. This +section described advanced options to be used with `--create'. + +* Menu: + +* override:: Overriding File Metadata. +* Ignore Failed Read:: + + +File: tar.info, Node: override, Next: Ignore Failed Read, Up: create options + +4.3.1 Overriding File Metadata +------------------------------ + +As described above, a `tar' archive keeps, for each member it contains, +its "metadata", such as modification time, mode and ownership of the +file. GNU `tar' allows to replace these data with other values when +adding files to the archive. The options described in this section +affect creation of archives of any type. For POSIX archives, see also +*note PAX keywords::, for additional ways of controlling metadata, +stored in the archive. + +`--mode=PERMISSIONS' + When adding files to an archive, `tar' will use PERMISSIONS for + the archive members, rather than the permissions from the files. + PERMISSIONS can be specified either as an octal number or as + symbolic permissions, like with `chmod' (*Note Permissions: + (fileutils)File permissions. This reference also has useful + information for those not being overly familiar with the UNIX + permission system). Using latter syntax allows for more + flexibility. For example, the value `a+rw' adds read and write + permissions for everybody, while retaining executable bits on + directories or on any other file already marked as executable: + + $ tar -c -f archive.tar --mode='a+rw' . + +`--mtime=DATE' + When adding files to an archive, `tar' will use DATE as the + modification time of members when creating archives, instead of + their actual modification times. The argument DATE can be either + a textual date representation in almost arbitrary format (*note + Date input formats::) or a name of the existing file, starting + with `/' or `.'. In the latter case, the modification time of + that file will be used. + + The following example will set the modification date to 00:00:00 + UTC, January 1, 1970: + + $ tar -c -f archive.tar --mtime='1970-01-01' . + + When used with `--verbose' (*note verbose tutorial::) GNU `tar' + will try to convert the specified date back to its textual + representation and compare it with the one given with `--mtime' + options. If the two dates differ, `tar' will print a warning + saying what date it will use. This is to help user ensure he is + using the right date. + + For example: + + $ tar -c -f archive.tar -v --mtime=yesterday . + tar: Option --mtime: Treating date `yesterday' as 2006-06-20 + 13:06:29.152478 + ... + +`--owner=USER' + Specifies that `tar' should use USER as the owner of members when + creating archives, instead of the user associated with the source + file. The argument USER can be either an existing user symbolic + name, or a decimal numeric user ID. + + There is no value indicating a missing number, and `0' usually + means `root'. Some people like to force `0' as the value to offer + in their distributions for the owner of files, because the `root' + user is anonymous anyway, so that might as well be the owner of + anonymous archives. For example: + + $ tar -c -f archive.tar --owner=0 . + # Or: + $ tar -c -f archive.tar --owner=root . + +`--group=GROUP' + Files added to the `tar' archive will have a group ID of GROUP, + rather than the group from the source file. The argument GROUP + can be either an existing group symbolic name, or a decimal + numeric group ID. + + +File: tar.info, Node: Ignore Failed Read, Prev: override, Up: create options + +4.3.2 Ignore Fail Read +---------------------- + +`--ignore-failed-read' + Do not exit with nonzero on unreadable files or directories. + + +File: tar.info, Node: extract options, Next: backup, Prev: create options, Up: operations + +4.4 Options Used by `--extract' +=============================== + + _(This message will disappear, once this node revised.)_ + +The previous chapter showed how to use `--extract' to extract an +archive into the file system. Various options cause `tar' to extract +more information than just file contents, such as the owner, the +permissions, the modification date, and so forth. This section +presents options to be used with `--extract' when certain special +considerations arise. You may review the information presented in +*note extract:: for more basic information about the `--extract' +operation. + +* Menu: + +* Reading:: Options to Help Read Archives +* Writing:: Changing How `tar' Writes Files +* Scarce:: Coping with Scarce Resources + + +File: tar.info, Node: Reading, Next: Writing, Up: extract options + +4.4.1 Options to Help Read Archives +----------------------------------- + + _(This message will disappear, once this node revised.)_ + +Normally, `tar' will request data in full record increments from an +archive storage device. If the device cannot return a full record, +`tar' will report an error. However, some devices do not always return +full records, or do not require the last record of an archive to be +padded out to the next record boundary. To keep reading until you +obtain a full record, or to accept an incomplete record if it contains +an end-of-archive marker, specify the `--read-full-records' (`-B') +option in conjunction with the `--extract' or `--list' operations. +*Note Blocking::. + + The `--read-full-records' (`-B') option is turned on by default when +`tar' reads an archive from standard input, or from a remote machine. +This is because on BSD Unix systems, attempting to read a pipe returns +however much happens to be in the pipe, even if it is less than was +requested. If this option were not enabled, `tar' would fail as soon +as it read an incomplete record from the pipe. + + If you're not sure of the blocking factor of an archive, you can +read the archive by specifying `--read-full-records' (`-B') and +`--blocking-factor=512-SIZE' (`-b 512-SIZE'), using a blocking factor +larger than what the archive uses. This lets you avoid having to +determine the blocking factor of an archive. *Note Blocking Factor::. + +* Menu: + +* read full records:: +* Ignore Zeros:: + + +File: tar.info, Node: read full records, Next: Ignore Zeros, Up: Reading + +Reading Full Records +.................... + +`--read-full-records' + +`-B' + Use in conjunction with `--extract' (`--get', `-x') to read an + archive which contains incomplete records, or one which has a + blocking factor less than the one specified. + + +File: tar.info, Node: Ignore Zeros, Prev: read full records, Up: Reading + +Ignoring Blocks of Zeros +........................ + +Normally, `tar' stops reading when it encounters a block of zeros +between file entries (which usually indicates the end of the archive). +`--ignore-zeros' (`-i') allows `tar' to completely read an archive +which contains a block of zeros before the end (i.e., a damaged +archive, or one that was created by concatenating several archives +together). + + The `--ignore-zeros' (`-i') option is turned off by default because +many versions of `tar' write garbage after the end-of-archive entry, +since that part of the media is never supposed to be read. GNU `tar' +does not write after the end of an archive, but seeks to maintain +compatibility among archiving utilities. + +`--ignore-zeros' +`-i' + To ignore blocks of zeros (i.e., end-of-archive entries) which may + be encountered while reading an archive. Use in conjunction with + `--extract' or `--list'. + + +File: tar.info, Node: Writing, Next: Scarce, Prev: Reading, Up: extract options + +4.4.2 Changing How `tar' Writes Files +------------------------------------- + + _(This message will disappear, once this node revised.)_ + +* Menu: + +* Dealing with Old Files:: +* Overwrite Old Files:: +* Keep Old Files:: +* Keep Newer Files:: +* Unlink First:: +* Recursive Unlink:: +* Data Modification Times:: +* Setting Access Permissions:: +* Directory Modification Times and Permissions:: +* Writing to Standard Output:: +* Writing to an External Program:: +* remove files:: + + +File: tar.info, Node: Dealing with Old Files, Next: Overwrite Old Files, Up: Writing + +Options Controlling the Overwriting of Existing Files +..................................................... + +When extracting files, if `tar' discovers that the extracted file +already exists, it normally replaces the file by removing it before +extracting it, to prevent confusion in the presence of hard or symbolic +links. (If the existing file is a symbolic link, it is removed, not +followed.) However, if a directory cannot be removed because it is +nonempty, `tar' normally overwrites its metadata (ownership, +permission, etc.). The `--overwrite-dir' option enables this default +behavior. To be more cautious and preserve the metadata of such a +directory, use the `--no-overwrite-dir' option. + + To be even more cautious and prevent existing files from being +replaced, use the `--keep-old-files' (`-k') option. It causes `tar' to +refuse to replace or update a file that already exists, i.e., a file +with the same name as an archive member prevents extraction of that +archive member. Instead, it reports an error. + + To be more aggressive about altering existing files, use the +`--overwrite' option. It causes `tar' to overwrite existing files and +to follow existing symbolic links when extracting. + + Some people argue that GNU `tar' should not hesitate to overwrite +files with other files when extracting. When extracting a `tar' +archive, they expect to see a faithful copy of the state of the file +system when the archive was created. It is debatable that this would +always be a proper behavior. For example, suppose one has an archive +in which `usr/local' is a link to `usr/local2'. Since then, maybe the +site removed the link and renamed the whole hierarchy from +`/usr/local2' to `/usr/local'. Such things happen all the time. I +guess it would not be welcome at all that GNU `tar' removes the whole +hierarchy just to make room for the link to be reinstated (unless it +_also_ simultaneously restores the full `/usr/local2', of course!) GNU +`tar' is indeed able to remove a whole hierarchy to reestablish a +symbolic link, for example, but _only if_ `--recursive-unlink' is +specified to allow this behavior. In any case, single files are +silently removed. + + Finally, the `--unlink-first' (`-U') option can improve performance +in some cases by causing `tar' to remove files unconditionally before +extracting them. + + +File: tar.info, Node: Overwrite Old Files, Next: Keep Old Files, Prev: Dealing with Old Files, Up: Writing + +Overwrite Old Files +................... + +`--overwrite' + Overwrite existing files and directory metadata when extracting + files from an archive. + + This causes `tar' to write extracted files into the file system + without regard to the files already on the system; i.e., files + with the same names as archive members are overwritten when the + archive is extracted. It also causes `tar' to extract the + ownership, permissions, and time stamps onto any preexisting files + or directories. If the name of a corresponding file name is a + symbolic link, the file pointed to by the symbolic link will be + overwritten instead of the symbolic link itself (if this is + possible). Moreover, special devices, empty directories and even + symbolic links are automatically removed if they are in the way of + extraction. + + Be careful when using the `--overwrite' option, particularly when + combined with the `--absolute-names' (`-P') option, as this + combination can change the contents, ownership or permissions of + any file on your system. Also, many systems do not take kindly to + overwriting files that are currently being executed. + +`--overwrite-dir' + Overwrite the metadata of directories when extracting files from an + archive, but remove other files before extracting. + + +File: tar.info, Node: Keep Old Files, Next: Keep Newer Files, Prev: Overwrite Old Files, Up: Writing + +Keep Old Files +.............. + +`--keep-old-files' +`-k' + Do not replace existing files from archive. The + `--keep-old-files' (`-k') option prevents `tar' from replacing + existing files with files with the same name from the archive. The + `--keep-old-files' option is meaningless with `--list' (`-t'). + Prevents `tar' from replacing files in the file system during + extraction. + + +File: tar.info, Node: Keep Newer Files, Next: Unlink First, Prev: Keep Old Files, Up: Writing + +Keep Newer Files +................ + +`--keep-newer-files' + Do not replace existing files that are newer than their archive + copies. This option is meaningless with `--list' (`-t'). + + +File: tar.info, Node: Unlink First, Next: Recursive Unlink, Prev: Keep Newer Files, Up: Writing + +Unlink First +............ + +`--unlink-first' +`-U' + Remove files before extracting over them. This can make `tar' run + a bit faster if you know in advance that the extracted files all + need to be removed. Normally this option slows `tar' down + slightly, so it is disabled by default. + + +File: tar.info, Node: Recursive Unlink, Next: Data Modification Times, Prev: Unlink First, Up: Writing + +Recursive Unlink +................ + +`--recursive-unlink' + When this option is specified, try removing files and directory + hierarchies before extracting over them. _This is a dangerous + option!_ + + If you specify the `--recursive-unlink' option, `tar' removes +_anything_ that keeps you from extracting a file as far as current +permissions will allow it. This could include removal of the contents +of a full directory hierarchy. + + +File: tar.info, Node: Data Modification Times, Next: Setting Access Permissions, Prev: Recursive Unlink, Up: Writing + +Setting Data Modification Times +............................... + +Normally, `tar' sets the data modification times of extracted files to +the corresponding times recorded for the files in the archive, but +limits the permissions of extracted files by the current `umask' +setting. + + To set the data modification times of extracted files to the time +when the files were extracted, use the `--touch' (`-m') option in +conjunction with `--extract' (`--get', `-x'). + +`--touch' +`-m' + Sets the data modification time of extracted archive members to + the time they were extracted, not the time recorded for them in + the archive. Use in conjunction with `--extract' (`--get', `-x'). + + +File: tar.info, Node: Setting Access Permissions, Next: Directory Modification Times and Permissions, Prev: Data Modification Times, Up: Writing + +Setting Access Permissions +.......................... + +To set the modes (access permissions) of extracted files to those +recorded for those files in the archive, use `--same-permissions' in +conjunction with the `--extract' (`--get', `-x') operation. + +`--preserve-permissions' +`--same-permissions' +`-p' + Set modes of extracted archive members to those recorded in the + archive, instead of current umask settings. Use in conjunction + with `--extract' (`--get', `-x'). + + +File: tar.info, Node: Directory Modification Times and Permissions, Next: Writing to Standard Output, Prev: Setting Access Permissions, Up: Writing + +Directory Modification Times and Permissions +............................................ + +After successfully extracting a file member, GNU `tar' normally +restores its permissions and modification times, as described in the +previous sections. This cannot be done for directories, because after +extracting a directory `tar' will almost certainly extract files into +that directory and this will cause the directory modification time to +be updated. Moreover, restoring that directory permissions may not +permit file creation within it. Thus, restoring directory permissions +and modification times must be delayed at least until all files have +been extracted into that directory. GNU `tar' restores directories +using the following approach. + + The extracted directories are created with the mode specified in the +archive, as modified by the umask of the user, which gives sufficient +permissions to allow file creation. The meta-information about the +directory is recorded in the temporary list of directories. When +preparing to extract next archive member, GNU `tar' checks if the +directory prefix of this file contains the remembered directory. If it +does not, the program assumes that all files have been extracted into +that directory, restores its modification time and permissions and +removes its entry from the internal list. This approach allows to +correctly restore directory meta-information in the majority of cases, +while keeping memory requirements sufficiently small. It is based on +the fact, that most `tar' archives use the predefined order of members: +first the directory, then all the files and subdirectories in that +directory. + + However, this is not always true. The most important exception are +incremental archives (*note Incremental Dumps::). The member order in +an incremental archive is reversed: first all directory members are +stored, followed by other (non-directory) members. So, when extracting +from incremental archives, GNU `tar' alters the above procedure. It +remembers all restored directories, and restores their meta-data only +after the entire archive has been processed. Notice, that you do not +need to specify any special options for that, as GNU `tar' +automatically detects archives in incremental format. + + There may be cases, when such processing is required for normal +archives too. Consider the following example: + + $ tar --no-recursion -cvf archive \ + foo foo/file1 bar bar/file foo/file2 + foo/ + foo/file1 + bar/ + bar/file + foo/file2 + + During the normal operation, after encountering `bar' GNU `tar' will +assume that all files from the directory `foo' were already extracted +and will therefore restore its timestamp and permission bits. However, +after extracting `foo/file2' the directory timestamp will be offset +again. + + To correctly restore directory meta-information in such cases, use +`delay-directory-restore' command line option: + +`--delay-directory-restore' + Delays restoring of the modification times and permissions of + extracted directories until the end of extraction. This way, + correct meta-information is restored even if the archive has + unusual member ordering. + +`--no-delay-directory-restore' + Cancel the effect of the previous `--delay-directory-restore'. + Use this option if you have used `--delay-directory-restore' in + `TAR_OPTIONS' variable (*note TAR_OPTIONS::) and wish to + temporarily disable it. + + +File: tar.info, Node: Writing to Standard Output, Next: Writing to an External Program, Prev: Directory Modification Times and Permissions, Up: Writing + +Writing to Standard Output +.......................... + +To write the extracted files to the standard output, instead of +creating the files on the file system, use `--to-stdout' (`-O') in +conjunction with `--extract' (`--get', `-x'). This option is useful if +you are extracting files to send them through a pipe, and do not need to +preserve them in the file system. If you extract multiple members, +they appear on standard output concatenated, in the order they are +found in the archive. + +`--to-stdout' +`-O' + Writes files to the standard output. Use only in conjunction with + `--extract' (`--get', `-x'). When this option is used, instead of + creating the files specified, `tar' writes the contents of the + files extracted to its standard output. This may be useful if you + are only extracting the files in order to send them through a + pipe. This option is meaningless with `--list' (`-t'). + + This can be useful, for example, if you have a tar archive containing +a big file and don't want to store the file on disk before processing +it. You can use a command like this: + + tar -xOzf foo.tgz bigfile | process + + or even like this if you want to process the concatenation of the +files: + + tar -xOzf foo.tgz bigfile1 bigfile2 | process + + However, `--to-command' may be more convenient for use with multiple +files. See the next section. + + +File: tar.info, Node: Writing to an External Program, Next: remove files, Prev: Writing to Standard Output, Up: Writing + +Writing to an External Program +.............................. + +You can instruct `tar' to send the contents of each extracted file to +the standard input of an external program: + +`--to-command=COMMAND' + Extract files and pipe their contents to the standard input of + COMMAND. When this option is used, instead of creating the files + specified, `tar' invokes COMMAND and pipes the contents of the + files to its standard output. COMMAND may contain command line + arguments. The program is executed via `sh -c'. Notice, that + COMMAND is executed once for each regular file extracted. + Non-regular files (directories, etc.) are ignored when this option + is used. + + The command can obtain the information about the file it processes +from the following environment variables: + +TAR_FILETYPE + Type of the file. It is a single letter with the following meaning: + + f Regular file + d Directory + l Symbolic link + h Hard link + b Block device + c Character device + + Currently only regular files are supported. + +TAR_MODE + File mode, an octal number. + +TAR_FILENAME + The name of the file. + +TAR_REALNAME + Name of the file as stored in the archive. + +TAR_UNAME + Name of the file owner. + +TAR_GNAME + Name of the file owner group. + +TAR_ATIME + Time of last access. It is a decimal number, representing seconds + since the epoch. If the archive provides times with nanosecond + precision, the nanoseconds are appended to the timestamp after a + decimal point. + +TAR_MTIME + Time of last modification. + +TAR_CTIME + Time of last status change. + +TAR_SIZE + Size of the file. + +TAR_UID + UID of the file owner. + +TAR_GID + GID of the file owner. + + In addition to these variables, `TAR_VERSION' contains the GNU `tar' +version number. + + If COMMAND exits with a non-0 status, `tar' will print an error +message similar to the following: + + tar: 2345: Child returned status 1 + + Here, `2345' is the PID of the finished process. + + If this behavior is not wanted, use `--ignore-command-error': + +`--ignore-command-error' + Ignore exit codes of subprocesses. Notice that if the program + exits on signal or otherwise terminates abnormally, the error + message will be printed even if this option is used. + +`--no-ignore-command-error' + Cancel the effect of any previous `--ignore-command-error' option. + This option is useful if you have set `--ignore-command-error' in + `TAR_OPTIONS' (*note TAR_OPTIONS::) and wish to temporarily cancel + it. + + +File: tar.info, Node: remove files, Prev: Writing to an External Program, Up: Writing + +Removing Files +.............. + +`--remove-files' + Remove files after adding them to the archive. + + +File: tar.info, Node: Scarce, Prev: Writing, Up: extract options + +4.4.3 Coping with Scarce Resources +---------------------------------- + + _(This message will disappear, once this node revised.)_ + +* Menu: + +* Starting File:: +* Same Order:: + + +File: tar.info, Node: Starting File, Next: Same Order, Up: Scarce + +Starting File +............. + +`--starting-file=NAME' +`-K NAME' + Starts an operation in the middle of an archive. Use in + conjunction with `--extract' (`--get', `-x') or `--list' (`-t'). + + If a previous attempt to extract files failed due to lack of disk +space, you can use `--starting-file=NAME' (`-K NAME') to start +extracting only after member NAME of the archive. This assumes, of +course, that there is now free space, or that you are now extracting +into a different file system. (You could also choose to suspend `tar', +remove unnecessary files from the file system, and then restart the +same `tar' operation. In this case, `--starting-file' is not necessary. +*Note Incremental Dumps::, *Note interactive::, and *note exclude::.) + + +File: tar.info, Node: Same Order, Prev: Starting File, Up: Scarce + +Same Order +.......... + +`--same-order' +`--preserve-order' +`-s' + To process large lists of file names on machines with small + amounts of memory. Use in conjunction with `--compare' (`--diff', + `-d'), `--list' (`-t') or `--extract' (`--get', `-x'). + + The `--same-order' (`--preserve-order', `-s') option tells `tar' +that the list of file names to be listed or extracted is sorted in the +same order as the files in the archive. This allows a large list of +names to be used, even on a small machine that would not otherwise be +able to hold all the names in memory at the same time. Such a sorted +list can easily be created by running `tar -t' on the archive and +editing its output. + + This option is probably never needed on modern computer systems. + + +File: tar.info, Node: backup, Next: Applications, Prev: extract options, Up: operations + +4.5 Backup options +================== + +GNU `tar' offers options for making backups of files before writing new +versions. These options control the details of these backups. They +may apply to the archive itself before it is created or rewritten, as +well as individual extracted members. Other GNU programs (`cp', +`install', `ln', and `mv', for example) offer similar options. + + Backup options may prove unexpectedly useful when extracting archives +containing many members having identical name, or when extracting +archives on systems having file name limitations, making different +members appear has having similar names through the side-effect of name +truncation. (This is true only if we have a good scheme for truncated +backup names, which I'm not sure at all: I suspect work is needed in +this area.) When any existing file is backed up before being +overwritten by extraction, then clashing files are automatically be +renamed to be unique, and the true name is kept for only the last file +of a series of clashing files. By using verbose mode, users may track +exactly what happens. + + At the detail level, some decisions are still experimental, and may +change in the future, we are waiting comments from our users. So, +please do not learn to depend blindly on the details of the backup +features. For example, currently, directories themselves are never +renamed through using these options, so, extracting a file over a +directory still has good chances to fail. Also, backup options apply +to created archives, not only to extracted members. For created +archives, backups will not be attempted when the archive is a block or +character device, or when it refers to a remote file. + + For the sake of simplicity and efficiency, backups are made by +renaming old files prior to creation or extraction, and not by copying. +The original name is restored if the file creation fails. If a +failure occurs after a partial extraction of a file, both the backup +and the partially extracted file are kept. + +`--backup[=METHOD]' + Back up files that are about to be overwritten or removed. + Without this option, the original versions are destroyed. + + Use METHOD to determine the type of backups made. If METHOD is + not specified, use the value of the `VERSION_CONTROL' environment + variable. And if `VERSION_CONTROL' is not set, use the `existing' + method. + + This option corresponds to the Emacs variable `version-control'; + the same values for METHOD are accepted as in Emacs. This option + also allows more descriptive names. The valid METHODs are: + + `t' + `numbered' + Always make numbered backups. + + `nil' + `existing' + Make numbered backups of files that already have them, simple + backups of the others. + + `never' + `simple' + Always make simple backups. + + +`--suffix=SUFFIX' + Append SUFFIX to each backup file made with `--backup'. If this + option is not specified, the value of the `SIMPLE_BACKUP_SUFFIX' + environment variable is used. And if `SIMPLE_BACKUP_SUFFIX' is not + set, the default is `~', just as in Emacs. + + + +File: tar.info, Node: Applications, Next: looking ahead, Prev: backup, Up: operations + +4.6 Notable `tar' Usages +======================== + + _(This message will disappear, once this node revised.)_ + +You can easily use archive files to transport a group of files from one +system to another: put all relevant files into an archive on one +computer system, transfer the archive to another system, and extract +the contents there. The basic transfer medium might be magnetic tape, +Internet FTP, or even electronic mail (though you must encode the +archive with `uuencode' in order to transport it properly by mail). +Both machines do not have to use the same operating system, as long as +they both support the `tar' program. + + For example, here is how you might copy a directory's contents from +one disk to another, while preserving the dates, modes, owners and +link-structure of all the files therein. In this case, the transfer +medium is a "pipe", which is one a Unix redirection mechanism: + + $ (cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -) + +You can avoid subshells by using `-C' option: + + $ tar -C sourcedir -cf - . | tar -C targetdir -xf - + +The command also works using short option forms: + + $ (cd sourcedir; tar --create --file=- . ) \ + | (cd targetdir; tar --extract --file=-) + # Or: + $ tar --directory sourcedir --create --file=- . ) \ + | tar --directory targetdir --extract --file=- + +This is one of the easiest methods to transfer a `tar' archive. + + +File: tar.info, Node: looking ahead, Prev: Applications, Up: operations + +4.7 Looking Ahead: The Rest of this Manual +========================================== + +You have now seen how to use all eight of the operations available to +`tar', and a number of the possible options. The next chapter explains +how to choose and change file and archive names, how to use files to +store names of other files which you can then call as arguments to +`tar' (this can help you save time if you expect to archive the same +list of files a number of times), and so forth. + + If there are too many files to conveniently list on the command line, +you can list the names in a file, and `tar' will read that file. *Note +files::. + + There are various ways of causing `tar' to skip over some files, and +not archive them. *Note Choosing::. + + +File: tar.info, Node: Backups, Next: Choosing, Prev: operations, Up: Top + +5 Performing Backups and Restoring Files +**************************************** + + _(This message will disappear, once this node revised.)_ + +GNU `tar' is distributed along with the scripts which the Free Software +Foundation uses for performing backups. There is no corresponding +scripts available yet for doing restoration of files. Even if there is +a good chance those scripts may be satisfying to you, they are not the +only scripts or methods available for doing backups and restore. You +may well create your own, or use more sophisticated packages dedicated +to that purpose. + + Some users are enthusiastic about `Amanda' (The Advanced Maryland +Automatic Network Disk Archiver), a backup system developed by James da +Silva `jds@cs.umd.edu' and available on many Unix systems. This is +free software, and it is available at these places: + + http://www.cs.umd.edu/projects/amanda/amanda.html + ftp://ftp.cs.umd.edu/pub/amanda + + This chapter documents both the provided shell scripts and `tar' +options which are more specific to usage as a backup tool. + + To "back up" a file system means to create archives that contain all +the files in that file system. Those archives can then be used to +restore any or all of those files (for instance if a disk crashes or a +file is accidentally deleted). File system "backups" are also called +"dumps". + +* Menu: + +* Full Dumps:: Using `tar' to Perform Full Dumps +* Incremental Dumps:: Using `tar' to Perform Incremental Dumps +* Backup Levels:: Levels of Backups +* Backup Parameters:: Setting Parameters for Backups and Restoration +* Scripted Backups:: Using the Backup Scripts +* Scripted Restoration:: Using the Restore Script + + +File: tar.info, Node: Full Dumps, Next: Incremental Dumps, Up: Backups + +5.1 Using `tar' to Perform Full Dumps +===================================== + + _(This message will disappear, once this node revised.)_ + +Full dumps should only be made when no other people or programs are +modifying files in the file system. If files are modified while `tar' +is making the backup, they may not be stored properly in the archive, +in which case you won't be able to restore them if you have to. (Files +not being modified are written with no trouble, and do not corrupt the +entire archive.) + + You will want to use the `--label=ARCHIVE-LABEL' (`-V +ARCHIVE-LABEL') option to give the archive a volume label, so you can +tell what this archive is even if the label falls off the tape, or +anything like that. + + Unless the file system you are dumping is guaranteed to fit on one +volume, you will need to use the `--multi-volume' (`-M') option. Make +sure you have enough tapes on hand to complete the backup. + + If you want to dump each file system separately you will need to use +the `--one-file-system' option to prevent `tar' from crossing file +system boundaries when storing (sub)directories. + + The `--incremental' (`-G') (*note Incremental Dumps::) option is not +needed, since this is a complete copy of everything in the file system, +and a full restore from this backup would only be done onto a completely +empty disk. + + Unless you are in a hurry, and trust the `tar' program (and your +tapes), it is a good idea to use the `--verify' (`-W') option, to make +sure your files really made it onto the dump properly. This will also +detect cases where the file was modified while (or just after) it was +being archived. Not all media (notably cartridge tapes) are capable of +being verified, unfortunately. + + +File: tar.info, Node: Incremental Dumps, Next: Backup Levels, Prev: Full Dumps, Up: Backups + +5.2 Using `tar' to Perform Incremental Dumps +============================================ + +"Incremental backup" is a special form of GNU `tar' archive that stores +additional metadata so that exact state of the file system can be +restored when extracting the archive. + + GNU `tar' currently offers two options for handling incremental +backups: `--listed-incremental=SNAPSHOT-FILE' (`-g SNAPSHOT-FILE') and +`--incremental' (`-G'). + + The option `--listed-incremental' instructs tar to operate on an +incremental archive with additional metadata stored in a standalone +file, called a "snapshot file". The purpose of this file is to help +determine which files have been changed, added or deleted since the +last backup, so that the next incremental backup will contain only +modified files. The name of the snapshot file is given as an argument +to the option: + +`--listed-incremental=FILE' +`-g FILE' + Handle incremental backups with snapshot data in FILE. + + To create an incremental backup, you would use +`--listed-incremental' together with `--create' (*note create::). For +example: + + $ tar --create \ + --file=archive.1.tar \ + --listed-incremental=/var/log/usr.snar \ + /usr + + This will create in `archive.1.tar' an incremental backup of the +`/usr' file system, storing additional metadata in the file +`/var/log/usr.snar'. If this file does not exist, it will be created. +The created archive will then be a "level 0 backup"; please see the +next section for more on backup levels. + + Otherwise, if the file `/var/log/usr.snar' exists, it determines +which files are modified. In this case only these files will be stored +in the archive. Suppose, for example, that after running the above +command, you delete file `/usr/doc/old' and create directory +`/usr/local/db' with the following contents: + + $ ls /usr/local/db + /usr/local/db/data + /usr/local/db/index + + Some time later you create another incremental backup. You will +then see: + + $ tar --create \ + --file=archive.2.tar \ + --listed-incremental=/var/log/usr.snar \ + /usr + tar: usr/local/db: Directory is new + usr/local/db/ + usr/local/db/data + usr/local/db/index + +The created archive `archive.2.tar' will contain only these three +members. This archive is called a "level 1 backup". Notice that +`/var/log/usr.snar' will be updated with the new data, so if you plan +to create more `level 1' backups, it is necessary to create a working +copy of the snapshot file before running `tar'. The above example will +then be modified as follows: + + $ cp /var/log/usr.snar /var/log/usr.snar-1 + $ tar --create \ + --file=archive.2.tar \ + --listed-incremental=/var/log/usr.snar-1 \ + /usr + + Incremental dumps depend crucially on time stamps, so the results are +unreliable if you modify a file's time stamps during dumping (e.g., +with the `--atime-preserve=replace' option), or if you set the clock +backwards. + + Metadata stored in snapshot files include device numbers, which, +obviously is supposed to be a non-volatile value. However, it turns +out that NFS devices have undependable values when an automounter gets +in the picture. This can lead to a great deal of spurious redumping in +incremental dumps, so it is somewhat useless to compare two NFS devices +numbers over time. The solution implemented currently is to considers +all NFS devices as being equal when it comes to comparing directories; +this is fairly gross, but there does not seem to be a better way to go. + + Note that incremental archives use `tar' extensions and may not be +readable by non-GNU versions of the `tar' program. + + To extract from the incremental dumps, use `--listed-incremental' +together with `--extract' option (*note extracting files::). In this +case, `tar' does not need to access snapshot file, since all the data +necessary for extraction are stored in the archive itself. So, when +extracting, you can give whatever argument to `--listed-incremental', +the usual practice is to use `--listed-incremental=/dev/null'. +Alternatively, you can use `--incremental', which needs no arguments. +In general, `--incremental' (`-G') can be used as a shortcut for +`--listed-incremental' when listing or extracting incremental backups +(for more information, regarding this option, *note incremental-op::). + + When extracting from the incremental backup GNU `tar' attempts to +restore the exact state the file system had when the archive was +created. In particular, it will _delete_ those files in the file +system that did not exist in their directories when the archive was +created. If you have created several levels of incremental files, then +in order to restore the exact contents the file system had when the +last level was created, you will need to restore from all backups in +turn. Continuing our example, to restore the state of `/usr' file +system, one would do(1): + + $ tar --extract \ + --listed-incremental=/dev/null \ + --file archive.1.tar + $ tar --extract \ + --listed-incremental=/dev/null \ + --file archive.2.tar + + To list the contents of an incremental archive, use `--list' (*note +list::), as usual. To obtain more information about the archive, use +`--listed-incremental' or `--incremental' combined with two `--verbose' +options(2): + + tar --list --incremental --verbose --verbose archive.tar + + This command will print, for each directory in the archive, the list +of files in that directory at the time the archive was created. This +information is put out in a format which is both human-readable and +unambiguous for a program: each file name is printed as + + X FILE + +where X is a letter describing the status of the file: `Y' if the file +is present in the archive, `N' if the file is not included in the +archive, or a `D' if the file is a directory (and is included in the +archive). *Note Dumpdir::, for the detailed description of dumpdirs +and status codes. Each such line is terminated by a newline character. +The last line is followed by an additional newline to indicate the end +of the data. + + The option `--incremental' (`-G') gives the same behavior as +`--listed-incremental' when used with `--list' and `--extract' options. +When used with `--create' option, it creates an incremental archive +without creating snapshot file. Thus, it is impossible to create +several levels of incremental backups with `--incremental' option. + + ---------- Footnotes ---------- + + (1) Notice, that since both archives were created without `-P' +option (*note absolute::), these commands should be run from the root +file system. + + (2) Two `--verbose' options were selected to avoid breaking usual +verbose listing output (`--list --verbose') when using in scripts. + + Versions of GNU `tar' up to 1.15.1 used to dump verbatim binary +contents of the DUMPDIR header (with terminating nulls) when +`--incremental' or `--listed-incremental' option was given, no matter +what the verbosity level. This behavior, and, especially, the binary +output it produced were considered inconvenient and were changed in +version 1.16 + + +File: tar.info, Node: Backup Levels, Next: Backup Parameters, Prev: Incremental Dumps, Up: Backups + +5.3 Levels of Backups +===================== + +An archive containing all the files in the file system is called a +"full backup" or "full dump". You could insure your data by creating a +full dump every day. This strategy, however, would waste a substantial +amount of archive media and user time, as unchanged files are daily +re-archived. + + It is more efficient to do a full dump only occasionally. To back up +files between full dumps, you can use "incremental dumps". A "level +one" dump archives all the files that have changed since the last full +dump. + + A typical dump strategy would be to perform a full dump once a week, +and a level one dump once a day. This means some versions of files +will in fact be archived more than once, but this dump strategy makes +it possible to restore a file system to within one day of accuracy by +only extracting two archives--the last weekly (full) dump and the last +daily (level one) dump. The only information lost would be in files +changed or created since the last daily backup. (Doing dumps more than +once a day is usually not worth the trouble). + + GNU `tar' comes with scripts you can use to do full and level-one +(actually, even level-two and so on) dumps. Using scripts (shell +programs) to perform backups and restoration is a convenient and +reliable alternative to typing out file name lists and `tar' commands +by hand. + + Before you use these scripts, you need to edit the file +`backup-specs', which specifies parameters used by the backup scripts +and by the restore script. This file is usually located in +`/etc/backup' directory. *Note Backup Parameters::, for its detailed +description. Once the backup parameters are set, you can perform +backups or restoration by running the appropriate script. + + The name of the backup script is `backup'. The name of the restore +script is `restore'. The following sections describe their use in +detail. + + _Please Note:_ The backup and restoration scripts are designed to be +used together. While it is possible to restore files by hand from an +archive which was created using a backup script, and to create an +archive by hand which could then be extracted using the restore script, +it is easier to use the scripts. *Note Incremental Dumps::, before +making such an attempt. + + +File: tar.info, Node: Backup Parameters, Next: Scripted Backups, Prev: Backup Levels, Up: Backups + +5.4 Setting Parameters for Backups and Restoration +================================================== + +The file `backup-specs' specifies backup parameters for the backup and +restoration scripts provided with `tar'. You must edit `backup-specs' +to fit your system configuration and schedule before using these +scripts. + + Syntactically, `backup-specs' is a shell script, containing mainly +variable assignments. However, any valid shell construct is allowed in +this file. Particularly, you may wish to define functions within that +script (e.g., see `RESTORE_BEGIN' below). For more information about +shell script syntax, please refer to the definition of the Shell +Command Language +(http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta +g_02). See also *note Bash Features: (bashref)Top. + + The shell variables controlling behavior of `backup' and `restore' +are described in the following subsections. + +* Menu: + +* General-Purpose Variables:: +* Magnetic Tape Control:: +* User Hooks:: +* backup-specs example:: An Example Text of `Backup-specs' + + +File: tar.info, Node: General-Purpose Variables, Next: Magnetic Tape Control, Up: Backup Parameters + +5.4.1 General-Purpose Variables +------------------------------- + + -- Backup variable: ADMINISTRATOR + The user name of the backup administrator. `Backup' scripts sends + a backup report to this address. + + -- Backup variable: BACKUP_HOUR + The hour at which the backups are done. This can be a number from + 0 to 23, or the time specification in form HOURS:MINUTES, or the + string `now'. + + This variable is used by `backup'. Its value may be overridden + using `--time' option (*note Scripted Backups::). + + -- Backup variable: TAPE_FILE + The device `tar' writes the archive to. If TAPE_FILE is a remote + archive (*note remote-dev::), backup script will suppose that your + `mt' is able to access remote devices. If RSH (*note RSH::) is + set, `--rsh-command' option will be added to invocations of `mt'. + + -- Backup variable: BLOCKING + The blocking factor `tar' will use when writing the dump archive. + *Note Blocking Factor::. + + -- Backup variable: BACKUP_DIRS + A list of file systems to be dumped (for `backup'), or restored + (for `restore'). You can include any directory name in the list + -- subdirectories on that file system will be included, regardless + of how they may look to other networked machines. Subdirectories + on other file systems will be ignored. + + The host name specifies which host to run `tar' on, and should + normally be the host that actually contains the file system. + However, the host machine must have GNU `tar' installed, and must + be able to access the directory containing the backup scripts and + their support files using the same file name that is used on the + machine where the scripts are run (i.e., what `pwd' will print + when in that directory on that machine). If the host that contains + the file system does not have this capability, you can specify + another host as long as it can access the file system through NFS. + + If the list of file systems is very long you may wish to put it in + a separate file. This file is usually named `/etc/backup/dirs', + but this name may be overridden in `backup-specs' using `DIRLIST' + variable. + + -- Backup variable: DIRLIST + The name of the file that contains a list of file systems to backup + or restore. By default it is `/etc/backup/dirs'. + + -- Backup variable: BACKUP_FILES + A list of individual files to be dumped (for `backup'), or restored + (for `restore'). These should be accessible from the machine on + which the backup script is run. + + If the list of file systems is very long you may wish to store it + in a separate file. This file is usually named + `/etc/backup/files', but this name may be overridden in + `backup-specs' using `FILELIST' variable. + + -- Backup variable: FILELIST + The name of the file that contains a list of individual files to + backup or restore. By default it is `/etc/backup/files'. + + -- Backup variable: MT + Full file name of `mt' binary. + + -- Backup variable: RSH + Full file name of `rsh' binary or its equivalent. You may wish to + set it to `ssh', to improve security. In this case you will have + to use public key authentication. + + -- Backup variable: RSH_COMMAND + Full file name of `rsh' binary on remote machines. This will be + passed via `--rsh-command' option to the remote invocation of GNU + `tar'. + + -- Backup variable: VOLNO_FILE + Name of temporary file to hold volume numbers. This needs to be + accessible by all the machines which have file systems to be + dumped. + + -- Backup variable: XLIST + Name of "exclude file list". An "exclude file list" is a file + located on the remote machine and containing the list of files to + be excluded from the backup. Exclude file lists are searched in + /etc/tar-backup directory. A common use for exclude file lists is + to exclude files containing security-sensitive information (e.g., + `/etc/shadow' from backups). + + This variable affects only `backup'. + + -- Backup variable: SLEEP_TIME + Time to sleep between dumps of any two successive file systems + + This variable affects only `backup'. + + -- Backup variable: DUMP_REMIND_SCRIPT + Script to be run when it's time to insert a new tape in for the + next volume. Administrators may want to tailor this script for + their site. If this variable isn't set, GNU `tar' will display + its built-in prompt, and will expect confirmation from the + console. For the description of the default prompt, see *note + change volume prompt::. + + + -- Backup variable: SLEEP_MESSAGE + Message to display on the terminal while waiting for dump time. + Usually this will just be some literal text. + + -- Backup variable: TAR + Full file name of the GNU `tar' executable. If this is not set, + backup scripts will search `tar' in the current shell path. + + +File: tar.info, Node: Magnetic Tape Control, Next: User Hooks, Prev: General-Purpose Variables, Up: Backup Parameters + +5.4.2 Magnetic Tape Control +--------------------------- + +Backup scripts access tape device using special "hook functions". +These functions take a single argument - the name of the tape device. +Their names are kept in the following variables: + + -- Backup variable: MT_BEGIN + The name of "begin" function. This function is called before + accessing the drive. By default it retensions the tape: + + MT_BEGIN=mt_begin + + mt_begin() { + mt -f "$1" retension + } + + -- Backup variable: MT_REWIND + The name of "rewind" function. The default definition is as + follows: + + MT_REWIND=mt_rewind + + mt_rewind() { + mt -f "$1" rewind + } + + + -- Backup variable: MT_OFFLINE + The name of the function switching the tape off line. By default + it is defined as follows: + + MT_OFFLINE=mt_offline + + mt_offline() { + mt -f "$1" offl + } + + -- Backup variable: MT_STATUS + The name of the function used to obtain the status of the archive + device, including error count. Default definition: + + MT_STATUS=mt_status + + mt_status() { + mt -f "$1" status + } + + +File: tar.info, Node: User Hooks, Next: backup-specs example, Prev: Magnetic Tape Control, Up: Backup Parameters + +5.4.3 User Hooks +---------------- + +"User hooks" are shell functions executed before and after each `tar' +invocation. Thus, there are "backup hooks", which are executed before +and after dumping each file system, and "restore hooks", executed +before and after restoring a file system. Each user hook is a shell +function taking four arguments: + + -- User Hook Function: hook LEVEL HOST FS FSNAME + Its arguments are: + + LEVEL + Current backup or restore level. + + HOST + Name or IP address of the host machine being dumped or + restored. + + FS + Full file name of the file system being dumped or restored. + + FSNAME + File system name with directory separators replaced with + colons. This is useful, e.g., for creating unique files. + + Following variables keep the names of user hook functions + + -- Backup variable: DUMP_BEGIN + Dump begin function. It is executed before dumping the file + system. + + -- Backup variable: DUMP_END + Executed after dumping the file system. + + -- Backup variable: RESTORE_BEGIN + Executed before restoring the file system. + + -- Backup variable: RESTORE_END + Executed after restoring the file system. + + +File: tar.info, Node: backup-specs example, Prev: User Hooks, Up: Backup Parameters + +5.4.4 An Example Text of `Backup-specs' +--------------------------------------- + +The following is an example of `backup-specs': + + # site-specific parameters for file system backup. + + ADMINISTRATOR=friedman + BACKUP_HOUR=1 + TAPE_FILE=/dev/nrsmt0 + + # Use `ssh' instead of the less secure `rsh' + RSH=/usr/bin/ssh + RSH_COMMAND=/usr/bin/ssh + + # Override MT_STATUS function: + my_status() { + mts -t $TAPE_FILE + } + MT_STATUS=my_status + + # Disable MT_OFFLINE function + MT_OFFLINE=: + + BLOCKING=124 + BACKUP_DIRS=" + albert:/fs/fsf + apple-gunkies:/gd + albert:/fs/gd2 + albert:/fs/gp + geech:/usr/jla + churchy:/usr/roland + albert:/ + albert:/usr + apple-gunkies:/ + apple-gunkies:/usr + gnu:/hack + gnu:/u + apple-gunkies:/com/mailer/gnu + apple-gunkies:/com/archive/gnu" + + BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]" + + +File: tar.info, Node: Scripted Backups, Next: Scripted Restoration, Prev: Backup Parameters, Up: Backups + +5.5 Using the Backup Scripts +============================ + +The syntax for running a backup script is: + + backup --level=LEVEL --time=TIME + + The `level' option requests the dump level. Thus, to produce a full +dump, specify `--level=0' (this is the default, so `--level' may be +omitted if its value is `0'). (1) + + The `--time' option determines when should the backup be run. TIME +may take three forms: + +HH:MM + The dump must be run at HH hours MM minutes. + +HH + The dump must be run at HH hours + +now + The dump must be run immediately. + + You should start a script with a tape or disk mounted. Once you +start a script, it prompts you for new tapes or disks as it needs them. +Media volumes don't have to correspond to archive files -- a +multi-volume archive can be started in the middle of a tape that +already contains the end of another multi-volume archive. The +`restore' script prompts for media by its archive volume, so to avoid +an error message you should keep track of which tape (or disk) contains +which volume of the archive (*note Scripted Restoration::). + + The backup scripts write two files on the file system. The first is +a record file in `/etc/tar-backup/', which is used by the scripts to +store and retrieve information about which files were dumped. This +file is not meant to be read by humans, and should not be deleted by +them. *Note Snapshot Files::, for a more detailed explanation of this +file. + + The second file is a log file containing the names of the file +systems and files dumped, what time the backup was made, and any error +messages that were generated, as well as how much space was left in the +media volume after the last volume of the archive was written. You +should check this log file after every backup. The file name is +`log-MM-DD-YYYY-level-N', where MM-DD-YYYY represents current date, and +N represents current dump level number. + + The script also prints the name of each system being dumped to the +standard output. + + Following is the full list of options accepted by `backup' script: + +`-l LEVEL' +`--level=LEVEL' + Do backup level LEVEL (default 0). + +`-f' +`--force' + Force backup even if today's log file already exists. + +`-v[LEVEL]' +`--verbose[=LEVEL]' + Set verbosity level. The higher the level is, the more debugging + information will be output during execution. Default LEVEL is + 100, which means the highest debugging level. + +`-t START-TIME' +`--time=START-TIME' + Wait till TIME, then do backup. + +`-h' +`--help' + Display short help message and exit. + +`-V' +`--version' + Display information about the program's name, version, origin and + legal status, all on standard output, and then exit successfully. + + ---------- Footnotes ---------- + + (1) For backward compatibility, the `backup' will also try to deduce +the requested dump level from the name of the script itself. If the +name consists of a string `level-' followed by a single decimal digit, +that digit is taken as the dump level number. Thus, you may create a +link from `backup' to `level-1' and then run `level-1' whenever you +need to create a level one dump. + + +File: tar.info, Node: Scripted Restoration, Prev: Scripted Backups, Up: Backups + +5.6 Using the Restore Script +============================ + +To restore files that were archived using a scripted backup, use the +`restore' script. Its usage is quite straightforward. In the simplest +form, invoke `restore --all', it will then restore all the file systems +and files specified in `backup-specs' (*note BACKUP_DIRS: +General-Purpose Variables.). + + You may select the file systems (and/or files) to restore by giving +`restore' list of "patterns" in its command line. For example, running + + restore 'albert:*' + +will restore all file systems on the machine `albert'. A more +complicated example: + + restore 'albert:*' '*:/var' + +This command will restore all file systems on the machine `albert' as +well as `/var' file system on all machines. + + By default `restore' will start restoring files from the lowest +available dump level (usually zero) and will continue through all +available dump levels. There may be situations where such a thorough +restore is not necessary. For example, you may wish to restore only +files from the recent level one backup. To do so, use `--level' +option, as shown in the example below: + + restore --level=1 + + The full list of options accepted by `restore' follows: + +`-a' +`--all' + Restore all file systems and files specified in `backup-specs' + +`-l LEVEL' +`--level=LEVEL' + Start restoring from the given backup level, instead of the + default 0. + +`-v[LEVEL]' +`--verbose[=LEVEL]' + Set verbosity level. The higher the level is, the more debugging + information will be output during execution. Default LEVEL is + 100, which means the highest debugging level. + +`-h' +`--help' + Display short help message and exit. + +`-V' +`--version' + Display information about the program's name, version, origin and + legal status, all on standard output, and then exit successfully. + + You should start the restore script with the media containing the +first volume of the archive mounted. The script will prompt for other +volumes as they are needed. If the archive is on tape, you don't need +to rewind the tape to to its beginning--if the tape head is positioned +past the beginning of the archive, the script will rewind the tape as +needed. *Note Tape Positioning::, for a discussion of tape positioning. + + *Warning:* The script will delete files from the active file + system if they were not in the file system when the archive was + made. + + *Note Incremental Dumps::, for an explanation of how the script makes +that determination. + + +File: tar.info, Node: Choosing, Next: Date input formats, Prev: Backups, Up: Top + +6 Choosing Files and Names for `tar' +************************************ + + _(This message will disappear, once this node revised.)_ + +Certain options to `tar' enable you to specify a name for your archive. +Other options let you decide which files to include or exclude from +the archive, based on when or whether files were modified, whether the +file names do or don't match specified patterns, or whether files are +in specified directories. + + This chapter discusses these options in detail. + +* Menu: + +* file:: Choosing the Archive's Name +* Selecting Archive Members:: +* files:: Reading Names from a File +* exclude:: Excluding Some Files +* wildcards:: Wildcards Patterns and Matching +* quoting styles:: Ways of Quoting Special Characters in Names +* transform:: Modifying File and Member Names +* after:: Operating Only on New Files +* recurse:: Descending into Directories +* one:: Crossing File System Boundaries + + +File: tar.info, Node: file, Next: Selecting Archive Members, Up: Choosing + +6.1 Choosing and Naming Archive Files +===================================== + + _(This message will disappear, once this node revised.)_ + +By default, `tar' uses an archive file name that was compiled when it +was built on the system; usually this name refers to some physical tape +drive on the machine. However, the person who installed `tar' on the +system may not have set the default to a meaningful value as far as +most users are concerned. As a result, you will usually want to tell +`tar' where to find (or create) the archive. The `--file=ARCHIVE-NAME' +(`-f ARCHIVE-NAME') option allows you to either specify or name a file +to use as the archive instead of the default archive file location. + +`--file=ARCHIVE-NAME' +`-f ARCHIVE-NAME' + Name the archive to create or operate on. Use in conjunction with + any operation. + + For example, in this `tar' command, + + $ tar -cvf collection.tar blues folk jazz + +`collection.tar' is the name of the archive. It must directly follow +the `-f' option, since whatever directly follows `-f' _will_ end up +naming the archive. If you neglect to specify an archive name, you may +end up overwriting a file in the working directory with the archive you +create since `tar' will use this file's name for the archive name. + + An archive can be saved as a file in the file system, sent through a +pipe or over a network, or written to an I/O device such as a tape, +floppy disk, or CD write drive. + + If you do not name the archive, `tar' uses the value of the +environment variable `TAPE' as the file name for the archive. If that +is not available, `tar' uses a default, compiled-in archive name, +usually that for tape unit zero (i.e., `/dev/tu00'). + + If you use `-' as an ARCHIVE-NAME, `tar' reads the archive from +standard input (when listing or extracting files), or writes it to +standard output (when creating an archive). If you use `-' as an +ARCHIVE-NAME when modifying an archive, `tar' reads the original +archive from its standard input and writes the entire new archive to +its standard output. + + The following example is a convenient way of copying directory +hierarchy from `sourcedir' to `targetdir'. + + $ (cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -) + + The `-C' option allows to avoid using subshells: + + $ tar -C sourcedir -cf - . | tar -C targetdir -xpf - + + In both examples above, the leftmost `tar' invocation archives the +contents of `sourcedir' to the standard output, while the rightmost one +reads this archive from its standard input and extracts it. The `-p' +option tells it to restore permissions of the extracted files. + + To specify an archive file on a device attached to a remote machine, +use the following: + + --file=HOSTNAME:/DEV/FILE-NAME + +`tar' will complete the remote connection, if possible, and prompt you +for a username and password. If you use +`--file=@HOSTNAME:/DEV/FILE-NAME', `tar' will complete the remote +connection, if possible, using your username as the username on the +remote machine. + + If the archive file name includes a colon (`:'), then it is assumed +to be a file on another machine. If the archive file is +`USER@HOST:FILE', then FILE is used on the host HOST. The remote host +is accessed using the `rsh' program, with a username of USER. If the +username is omitted (along with the `@' sign), then your user name will +be used. (This is the normal `rsh' behavior.) It is necessary for the +remote machine, in addition to permitting your `rsh' access, to have +the `rmt' program installed (This command is included in the GNU `tar' +distribution and by default is installed under `PREFIX/libexec/rmt', +were PREFIX means your installation prefix). If you need to use a file +whose name includes a colon, then the remote tape drive behavior can be +inhibited by using the `--force-local' option. + + When the archive is being created to `/dev/null', GNU `tar' tries to +minimize input and output operations. The Amanda backup system, when +used with GNU `tar', has an initial sizing pass which uses this feature. + + +File: tar.info, Node: Selecting Archive Members, Next: files, Prev: file, Up: Choosing + +6.2 Selecting Archive Members +============================= + +"File Name arguments" specify which files in the file system `tar' +operates on, when creating or adding to an archive, or which archive +members `tar' operates on, when reading or deleting from an archive. +*Note Operations::. + + To specify file names, you can include them as the last arguments on +the command line, as follows: + tar OPERATION [OPTION1 OPTION2 ...] [FILE NAME-1 FILE NAME-2 ...] + + If a file name begins with dash (`-'), precede it with `--add-file' +option to prevent it from being treated as an option. + + By default GNU `tar' attempts to "unquote" each file or member name, +replacing "escape sequences" according to the following table: + +Escape Replaced with +----------------------------------------------------------- +\a Audible bell (ASCII 7) +\b Backspace (ASCII 8) +\f Form feed (ASCII 12) +\n New line (ASCII 10) +\r Carriage return (ASCII 13) +\t Horizontal tabulation (ASCII 9) +\v Vertical tabulation (ASCII 11) +\? ASCII 127 +\N ASCII N (N should be an octal number + of up to 3 digits) + + A backslash followed by any other symbol is retained. + + This default behavior is controlled by the following command line +option: + +`--unquote' + Enable unquoting input file or member names (default). + +`--no-unquote' + Disable unquoting input file or member names. + + If you specify a directory name as a file name argument, all the +files in that directory are operated on by `tar'. + + If you do not specify files, `tar' behavior differs depending on the +operation mode as described below: + + When `tar' is invoked with `--create' (`-c'), `tar' will stop +immediately, reporting the following: + + $ tar cf a.tar + tar: Cowardly refusing to create an empty archive + Try `tar --help' or `tar --usage' for more information. + + If you specify either `--list' (`-t') or `--extract' (`--get', +`-x'), `tar' operates on all the archive members in the archive. + + If run with `--diff' option, tar will compare the archive with the +contents of the current working directory. + + If you specify any other operation, `tar' does nothing. + + By default, `tar' takes file names from the command line. However, +there are other ways to specify file or member names, or to modify the +manner in which `tar' selects the files or members upon which to +operate. In general, these methods work both for specifying the names +of files and archive members. + + +File: tar.info, Node: files, Next: exclude, Prev: Selecting Archive Members, Up: Choosing + +6.3 Reading Names from a File +============================= + +Instead of giving the names of files or archive members on the command +line, you can put the names into a file, and then use the +`--files-from=FILE-OF-NAMES' (`-T FILE-OF-NAMES') option to `tar'. +Give the name of the file which contains the list of files to include +as the argument to `--files-from'. In the list, the file names should +be separated by newlines. You will frequently use this option when you +have generated the list of files to archive with the `find' utility. + +`--files-from=FILE-NAME' +`-T FILE-NAME' + Get names to extract or create from file FILE-NAME. + + If you give a single dash as a file name for `--files-from', (i.e., +you specify either `--files-from=-' or `-T -'), then the file names are +read from standard input. + + Unless you are running `tar' with `--create', you can not use both +`--files-from=-' and `--file=-' (`-f -') in the same command. + + Any number of `-T' options can be given in the command line. + + The following example shows how to use `find' to generate a list of +files smaller than 400K in length and put that list into a file called +`small-files'. You can then use the `-T' option to `tar' to specify +the files from that file, `small-files', to create the archive +`little.tgz'. (The `-z' option to `tar' compresses the archive with +`gzip'; *note gzip:: for more information.) + + $ find . -size -400 -print > small-files + $ tar -c -v -z -T small-files -f little.tgz + +In the file list given by `-T' option, any file name beginning with `-' +character is considered a `tar' option and is processed accordingly.(1) +For example, the common use of this feature is to change to another +directory by specifying `-C' option: + + $ cat list + -C/etc + passwd + hosts + -C/lib + libc.a + $ tar -c -f foo.tar --files-from list + +In this example, `tar' will first switch to `/etc' directory and add +files `passwd' and `hosts' to the archive. Then it will change to +`/lib' directory and will archive the file `libc.a'. Thus, the +resulting archive `foo.tar' will contain: + + $ tar tf foo.tar + passwd + hosts + libc.a + + + Notice that the option parsing algorithm used with `-T' is stricter +than the one used by shell. Namely, when specifying option arguments, +you should observe the following rules: + + * When using short (single-letter) option form, its argument must + immediately follow the option letter, without any intervening + whitespace. For example: `-Cdir'. + + * When using long option form, the option argument must be separated + from the option by a single equal sign. No whitespace is allowed + on any side of the equal sign. For example: `--directory=dir'. + + * For both short and long option forms, the option argument can be + given on the next line after the option name, e.g.: + + --directory + dir + + and + + -C + dir + + If you happen to have a file whose name starts with `-', precede it +with `--add-file' option to prevent it from being recognized as an +option. For example: `--add-file=--my-file'. + +* Menu: + +* nul:: + + ---------- Footnotes ---------- + + (1) Versions of GNU `tar' up to 1.15.1 recognized only `-C' option +in file lists, and only if the option and its argument occupied two +consecutive lines. + + +File: tar.info, Node: nul, Up: files + +6.3.1 `NUL' Terminated File Names +--------------------------------- + +The `--null' option causes `--files-from=FILE-OF-NAMES' (`-T +FILE-OF-NAMES') to read file names terminated by a `NUL' instead of a +newline, so files whose names contain newlines can be archived using +`--files-from'. + +`--null' + Only consider `NUL' terminated file names, instead of files that + terminate in a newline. + + The `--null' option is just like the one in GNU `xargs' and `cpio', +and is useful with the `-print0' predicate of GNU `find'. In `tar', +`--null' also disables special handling for file names that begin with +dash. + + This example shows how to use `find' to generate a list of files +larger than 800K in length and put that list into a file called +`long-files'. The `-print0' option to `find' is just like `-print', +except that it separates files with a `NUL' rather than with a newline. +You can then run `tar' with both the `--null' and `-T' options to +specify that `tar' get the files from that file, `long-files', to +create the archive `big.tgz'. The `--null' option to `tar' will cause +`tar' to recognize the `NUL' separator between files. + + $ find . -size +800 -print0 > long-files + $ tar -c -v --null --files-from=long-files --file=big.tar + + +File: tar.info, Node: exclude, Next: wildcards, Prev: files, Up: Choosing + +6.4 Excluding Some Files +======================== + + _(This message will disappear, once this node revised.)_ + +To avoid operating on files whose names match a particular pattern, use +the `--exclude' or `--exclude-from' options. + +`--exclude=PATTERN' + Causes `tar' to ignore files that match the PATTERN. + + The `--exclude=PATTERN' option prevents any file or member whose +name matches the shell wildcard (PATTERN) from being operated on. For +example, to create an archive with all the contents of the directory +`src' except for files whose names end in `.o', use the command `tar +-cf src.tar --exclude='*.o' src'. + + You may give multiple `--exclude' options. + +`--exclude-from=FILE' +`-X FILE' + Causes `tar' to ignore files that match the patterns listed in + FILE. + + Use the `--exclude-from' option to read a list of patterns, one per +line, from FILE; `tar' will ignore files matching those patterns. Thus +if `tar' is called as `tar -c -X foo .' and the file `foo' contains a +single line `*.o', no files whose names end in `.o' will be added to +the archive. + + When creating an archive, the `--exclude-caches' option family +causes `tar' to exclude all directories that contain a "cache directory +tag". A cache directory tag is a short file with the well-known name +`CACHEDIR.TAG' and having a standard header specified in +`http://www.brynosaurus.com/cachedir/spec.html'. Various applications +write cache directory tags into directories they use to hold +regenerable, non-precious data, so that such data can be more easily +excluded from backups. + + There are three `exclude-caches' option, providing a different +exclusion semantics: + +`--exclude-caches' + Do not archive the contents of the directory, but archive the + directory itself and the `CACHEDIR.TAG' file. + +`--exclude-caches-under' + Do not archive the contents of the directory, nor the + `CACHEDIR.TAG' file, archive only the directory itself. + +`--exclude-caches-all' + Omit directories containing `CACHEDIR.TAG' file entirely. + + Another option family, `--exclude-tag', provides a generalization of +this concept. It takes a single argument, a file name to look for. +Any directory that contains this file will be excluded from the dump. +Similarly to `exclude-caches', there are three options in this option +family: + +`--exclude-tag=FILE' + Do not dump the contents of the directory, but dump the directory + itself and the FILE. + +`--exclude-tag-under=FILE' + Do not dump the contents of the directory, nor the FILE, archive + only the directory itself. + +`--exclude-tag-all=FILE' + Omit directories containing FILE file entirely. + + Multiple `--exclude-tag*' options can be given. + + For example, given this directory: + + $ find dir + dir + dir/blues + dir/jazz + dir/folk + dir/folk/tagfile + dir/folk/sanjuan + dir/folk/trote + + The `--exclude-tag' will produce the following: + + $ tar -cf archive.tar --exclude-tag=tagfile -v dir + dir/ + dir/blues + dir/jazz + dir/folk/ + tar: dir/folk/: contains a cache directory tag tagfile; + contents not dumped + dir/folk/tagfile + + Both the `dir/folk' directory and its tagfile are preserved in the +archive, however the rest of files in this directory are not. + + Now, using the `--exclude-tag-under' option will exclude `tagfile' +from the dump, while still preserving the directory itself, as shown in +this example: + + $ tar -cf archive.tar --exclude-tag-under=tagfile -v dir + dir/ + dir/blues + dir/jazz + dir/folk/ + ./tar: dir/folk/: contains a cache directory tag tagfile; + contents not dumped + + Finally, using `--exclude-tag-all' omits the `dir/folk' directory +entirely: + + $ tar -cf archive.tar --exclude-tag-all=tagfile -v dir + dir/ + dir/blues + dir/jazz + ./tar: dir/folk/: contains a cache directory tag tagfile; + directory not dumped + +* Menu: + +* problems with exclude:: + + +File: tar.info, Node: problems with exclude, Up: exclude + +Problems with Using the `exclude' Options +----------------------------------------- + +Some users find `exclude' options confusing. Here are some common +pitfalls: + + * The main operating mode of `tar' does not act on a file name + explicitly listed on the command line, if one of its file name + components is excluded. In the example above, if you create an + archive and exclude files that end with `*.o', but explicitly name + the file `dir.o/foo' after all the options have been listed, + `dir.o/foo' will be excluded from the archive. + + * You can sometimes confuse the meanings of `--exclude' and + `--exclude-from'. Be careful: use `--exclude' when files to be + excluded are given as a pattern on the command line. Use + `--exclude-from' to introduce the name of a file which contains a + list of patterns, one per line; each of these patterns can exclude + zero, one, or many files. + + * When you use `--exclude=PATTERN', be sure to quote the PATTERN + parameter, so GNU `tar' sees wildcard characters like `*'. If you + do not do this, the shell might expand the `*' itself using files + at hand, so `tar' might receive a list of files instead of one + pattern, or none at all, making the command somewhat illegal. + This might not correspond to what you want. + + For example, write: + + $ tar -c -f ARCHIVE.TAR --exclude '*.o' DIRECTORY + + rather than: + + # _Wrong!_ + $ tar -c -f ARCHIVE.TAR --exclude *.o DIRECTORY + + * You must use use shell syntax, or globbing, rather than `regexp' + syntax, when using exclude options in `tar'. If you try to use + `regexp' syntax to describe files to be excluded, your command + might fail. + + * In earlier versions of `tar', what is now the `--exclude-from' + option was called `--exclude' instead. Now, `--exclude' applies + to patterns listed on the command line and `--exclude-from' + applies to patterns listed in a file. + + + +File: tar.info, Node: wildcards, Next: quoting styles, Prev: exclude, Up: Choosing + +6.5 Wildcards Patterns and Matching +=================================== + +"Globbing" is the operation by which "wildcard" characters, `*' or `?' +for example, are replaced and expanded into all existing files matching +the given pattern. GNU `tar' can use wildcard patterns for matching +(or globbing) archive members when extracting from or listing an +archive. Wildcard patterns are also used for verifying volume labels +of `tar' archives. This section has the purpose of explaining wildcard +syntax for `tar'. + + A PATTERN should be written according to shell syntax, using wildcard +characters to effect globbing. Most characters in the pattern stand +for themselves in the matched string, and case is significant: `a' will +match only `a', and not `A'. The character `?' in the pattern matches +any single character in the matched string. The character `*' in the +pattern matches zero, one, or more single characters in the matched +string. The character `\' says to take the following character of the +pattern _literally_; it is useful when one needs to match the `?', `*', +`[' or `\' characters, themselves. + + The character `[', up to the matching `]', introduces a character +class. A "character class" is a list of acceptable characters for the +next single character of the matched string. For example, `[abcde]' +would match any of the first five letters of the alphabet. Note that +within a character class, all of the "special characters" listed above +other than `\' lose their special meaning; for example, `[-\\[*?]]' +would match any of the characters, `-', `\', `[', `*', `?', or `]'. +(Due to parsing constraints, the characters `-' and `]' must either +come _first_ or _last_ in a character class.) + + If the first character of the class after the opening `[' is `!' or +`^', then the meaning of the class is reversed. Rather than listing +character to match, it lists those characters which are _forbidden_ as +the next single character of the matched string. + + Other characters of the class stand for themselves. The special +construction `[A-E]', using an hyphen between two letters, is meant to +represent all characters between A and E, inclusive. + + Periods (`.') or forward slashes (`/') are not considered special +for wildcard matches. However, if a pattern completely matches a +directory prefix of a matched string, then it matches the full matched +string: thus, excluding a directory also excludes all the files beneath +it. + +* Menu: + +* controlling pattern-matching:: + + +File: tar.info, Node: controlling pattern-matching, Up: wildcards + +Controlling Pattern-Matching +---------------------------- + +For the purposes of this section, we call "exclusion members" all +member names obtained while processing `--exclude' and `--exclude-from' +options, and "inclusion members" those member names that were given in +the command line or read from the file specified with `--files-from' +option. + + These two pairs of member lists are used in the following operations: +`--diff', `--extract', `--list', `--update'. + + There are no inclusion members in create mode (`--create' and +`--append'), since in this mode the names obtained from the command +line refer to _files_, not archive members. + + By default, inclusion members are compared with archive members +literally (1) and exclusion members are treated as globbing patterns. +For example: + + $ tar tf foo.tar + a.c + b.c + a.txt + [remarks] + # Member names are used verbatim: + $ tar -xf foo.tar -v '[remarks]' + [remarks] + # Exclude member names are globbed: + $ tar -xf foo.tar -v --exclude '*.c' + a.txt + [remarks] + + This behavior can be altered by using the following options: + +`--wildcards' + Treat all member names as wildcards. + +`--no-wildcards' + Treat all member names as literal strings. + + Thus, to extract files whose names end in `.c', you can use: + + $ tar -xf foo.tar -v --wildcards '*.c' + a.c + b.c + +Notice quoting of the pattern to prevent the shell from interpreting it. + + The effect of `--wildcards' option is canceled by `--no-wildcards'. +This can be used to pass part of the command line arguments verbatim +and other part as globbing patterns. For example, the following +invocation: + + $ tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]' + +instructs `tar' to extract from `foo.tar' all files whose names end in +`.txt' and the file named `[remarks]'. + + Normally, a pattern matches a name if an initial subsequence of the +name's components matches the pattern, where `*', `?', and `[...]' are +the usual shell wildcards, `\' escapes wildcards, and wildcards can +match `/'. + + Other than optionally stripping leading `/' from names (*note +absolute::), patterns and names are used as-is. For example, trailing +`/' is not trimmed from a user-specified name before deciding whether +to exclude it. + + However, this matching procedure can be altered by the options listed +below. These options accumulate. For example: + + --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme' + +ignores case when excluding `makefile', but not when excluding `readme'. + +`--anchored' +`--no-anchored' + If anchored, a pattern must match an initial subsequence of the + name's components. Otherwise, the pattern can match any + subsequence. Default is `--no-anchored' for exclusion members and + `--anchored' inclusion members. + +`--ignore-case' +`--no-ignore-case' + When ignoring case, upper-case patterns match lower-case names and + vice versa. When not ignoring case (the default), matching is + case-sensitive. + +`--wildcards-match-slash' +`--no-wildcards-match-slash' + When wildcards match slash (the default for exclusion members), a + wildcard like `*' in the pattern can match a `/' in the name. + Otherwise, `/' is matched only by `/'. + + + The `--recursion' and `--no-recursion' options (*note recurse::) +also affect how member patterns are interpreted. If recursion is in +effect, a pattern matches a name if it matches any of the name's parent +directories. + + The following table summarizes pattern-matching default values: + +Members Default settings +-------------------------------------------------------------------------- +Inclusion `--no-wildcards --anchored + --no-wildcards-match-slash' +Exclusion `--wildcards --no-anchored + --wildcards-match-slash' + + ---------- Footnotes ---------- + + (1) Notice that earlier GNU `tar' versions used globbing for +inclusion members, which contradicted to UNIX98 specification and was +not documented. *Note Changes::, for more information on this and other +changes. + + +File: tar.info, Node: quoting styles, Next: transform, Prev: wildcards, Up: Choosing + +6.6 Quoting Member Names +======================== + +When displaying member names, `tar' takes care to avoid ambiguities +caused by certain characters. This is called "name quoting". The +characters in question are: + + * Non-printable control characters: + + Character ASCII Character name + --------------------------------------------------------------- + \a 7 Audible bell + \b 8 Backspace + \f 12 Form feed + \n 10 New line + \r 13 Carriage return + \t 9 Horizontal tabulation + \v 11 Vertical tabulation + + * Space (ASCII 32) + + * Single and double quotes (`'' and `"') + + * Backslash (`\') + + The exact way `tar' uses to quote these characters depends on the +"quoting style". The default quoting style, called "escape" (see +below), uses backslash notation to represent control characters, space +and backslash. Using this quoting style, control characters are +represented as listed in column `Character' in the above table, a space +is printed as `\ ' and a backslash as `\\'. + + GNU `tar' offers seven distinct quoting styles, which can be selected +using `--quoting-style' option: + +`--quoting-style=STYLE' + Sets quoting style. Valid values for STYLE argument are: literal, + shell, shell-always, c, escape, locale, clocale. + + These styles are described in detail below. To illustrate their +effect, we will use an imaginary tar archive `arch.tar' containing the +following members: + + # 1. Contains horizontal tabulation character. + a tab + # 2. Contains newline character + a + newline + # 3. Contains a space + a space + # 4. Contains double quotes + a"double"quote + # 5. Contains single quotes + a'single'quote + # 6. Contains a backslash character: + a\backslash + + Here is how usual `ls' command would have listed them, if they had +existed in the current working directory: + + $ ls + a\ttab + a\nnewline + a\ space + a"double"quote + a'single'quote + a\\backslash + + Quoting styles: + +`literal' + No quoting, display each character as is: + + $ tar tf arch.tar --quoting-style=literal + ./ + ./a space + ./a'single'quote + ./a"double"quote + ./a\backslash + ./a tab + ./a + newline + +`shell' + Display characters the same way Bourne shell does: control + characters, except `\t' and `\n', are printed using backslash + escapes, `\t' and `\n' are printed as is, and a single quote is + printed as `\''. If a name contains any quoted characters, it is + enclosed in single quotes. In particular, if a name contains + single quotes, it is printed as several single-quoted strings: + + $ tar tf arch.tar --quoting-style=shell + ./ + './a space' + './a'\''single'\''quote' + './a"double"quote' + './a\backslash' + './a tab' + './a + newline' + +`shell-always' + Same as `shell', but the names are always enclosed in single + quotes: + + $ tar tf arch.tar --quoting-style=shell-always + './' + './a space' + './a'\''single'\''quote' + './a"double"quote' + './a\backslash' + './a tab' + './a + newline' + +`c' + Use the notation of the C programming language. All names are + enclosed in double quotes. Control characters are quoted using + backslash notations, double quotes are represented as `\"', + backslash characters are represented as `\\'. Single quotes and + spaces are not quoted: + + $ tar tf arch.tar --quoting-style=c + "./" + "./a space" + "./a'single'quote" + "./a\"double\"quote" + "./a\\backslash" + "./a\ttab" + "./a\nnewline" + +`escape' + Control characters are printed using backslash notation, a space is + printed as `\ ' and a backslash as `\\'. This is the default + quoting style, unless it was changed when configured the package. + + $ tar tf arch.tar --quoting-style=escape + ./ + ./a space + ./a'single'quote + ./a"double"quote + ./a\\backslash + ./a\ttab + ./a\nnewline + +`locale' + Control characters, single quote and backslash are printed using + backslash notation. All names are quoted using left and right + quotation marks, appropriate to the current locale. If it does not + define quotation marks, use ``' as left and `'' as right quotation + marks. Any occurrences of the right quotation mark in a name are + escaped with `\', for example: + + For example: + + $ tar tf arch.tar --quoting-style=locale + `./' + `./a space' + `./a\'single\'quote' + `./a"double"quote' + `./a\\backslash' + `./a\ttab' + `./a\nnewline' + +`clocale' + Same as `locale', but `"' is used for both left and right + quotation marks, if not provided by the currently selected locale: + + $ tar tf arch.tar --quoting-style=clocale + "./" + "./a space" + "./a'single'quote" + "./a\"double\"quote" + "./a\\backslash" + "./a\ttab" + "./a\nnewline" + + You can specify which characters should be quoted in addition to +those implied by the current quoting style: + +`--quote-chars=STRING' + Always quote characters from STRING, even if the selected quoting + style would not quote them. + + For example, using `escape' quoting (compare with the usual escape +listing above): + + $ tar tf arch.tar --quoting-style=escape --quote-chars=' "' + ./ + ./a\ space + ./a'single'quote + ./a\"double\"quote + ./a\\backslash + ./a\ttab + ./a\nnewline + + To disable quoting of such additional characters, use the following +option: + +`--no-quote-chars=STRING' + Remove characters listed in STRING from the list of quoted + characters set by the previous `--quote-chars' option. + + This option is particularly useful if you have added `--quote-chars' +to your `TAR_OPTIONS' (*note TAR_OPTIONS::) and wish to disable it for +the current invocation. + + Note, that `--no-quote-chars' does _not_ disable those characters +that are quoted by default in the selected quoting style. + + +File: tar.info, Node: transform, Next: after, Prev: quoting styles, Up: Choosing + +6.7 Modifying File and Member Names +=================================== + +`Tar' archives contain detailed information about files stored in them +and full file names are part of that information. When storing file to +an archive, its file name is recorded in the archive along with the +actual file contents. When restoring from an archive, a file is +created on disk with exactly the same name as that stored in the +archive. In the majority of cases this is the desired behavior of a +file archiver. However, there are some cases when it is not. + + First of all, it is often unsafe to extract archive members with +absolute file names or those that begin with a `../'. GNU `tar' takes +special precautions when extracting such names and provides a special +option for handling them, which is described in *note absolute::. + + Secondly, you may wish to extract file names without some leading +directory components, or with otherwise modified names. In other cases +it is desirable to store files under differing names in the archive. + + GNU `tar' provides two options for these needs. + +`--strip-components=NUMBER' + Strip given NUMBER of leading components from file names before + extraction. + + For example, suppose you have archived whole `/usr' hierarchy to a +tar archive named `usr.tar'. Among other files, this archive contains +`usr/include/stdlib.h', which you wish to extract to the current +working directory. To do so, you type: + + $ tar -xf usr.tar --strip=2 usr/include/stdlib.h + + The option `--strip=2' instructs `tar' to strip the two leading +components (`usr/' and `include/') off the file name. + + If you add to the above invocation `--verbose' (`-v') option, you +will note that the verbose listing still contains the full file name, +with the two removed components still in place. This can be +inconvenient, so `tar' provides a special option for altering this +behavior: + +`--show-transformed-names' + Display file or member names with all requested transformations + applied. + +For example: + + $ tar -xf usr.tar -v --strip=2 usr/include/stdlib.h + usr/include/stdlib.h + $ tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h + stdlib.h + + Notice that in both cases the file is `stdlib.h' extracted to the +current working directory, `--show-transformed-names' affects only the +way its name is displayed. + + This option is especially useful for verifying whether the invocation +will have the desired effect. Thus, before running + + $ tar -x --strip=N + +it is often advisable to run + + $ tar -t -v --show-transformed --strip=N + +to make sure the command will produce the intended results. + + In case you need to apply more complex modifications to the file +name, GNU `tar' provides a general-purpose transformation option: + +`--transform=EXPRESSION' + Modify file names using supplied EXPRESSION. + +The EXPRESSION is a `sed'-like replace expression of the form: + + s/REGEXP/REPLACE/[FLAGS] + +where REGEXP is a "regular expression", REPLACE is a replacement for +each file name part that matches REGEXP. Both REGEXP and REPLACE are +described in detail in *note The "s" Command: (sed)The "s" Command. + + Supported FLAGS are: + +`g' + Apply the replacement to _all_ matches to the REGEXP, not just the + first. + +`i' + Use case-insensitive matching + +`x' + REGEXP is an "extended regular expression" (*note Extended regular + expressions: (sed)Extended regexps.). + +`NUMBER' + Only replace the NUMBERth match of the REGEXP. + + Note: the POSIX standard does not specify what should happen when + you mix the `g' and NUMBER modifiers. GNU `tar' follows the GNU + `sed' implementation in this regard, so the interaction is defined + to be: ignore matches before the NUMBERth, and then match and + replace all matches from the NUMBERth on. + + + Any delimiter can be used in lieue of `/', the only requirement being +that it be used consistently throughout the expression. For example, +the following two expressions are equivalent: + + s/one/two/ + s,one,two, + + Changing delimiters is often useful when the REGEX contains slashes. +For example, it is more convenient to write `s,/,-,' than `s/\//-/'. + + Here are several examples of `--transform' usage: + + 1. Extract `usr/' hierarchy into `usr/local/': + + $ tar --transform='s,usr/,usr/local/,' -x -f arch.tar + + 2. Strip two leading directory components (equivalent to + `--strip-components=2'): + + $ tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar + + 3. Prepend `/prefix/' to each file name: + + $ tar --transform 's,^,/prefix/,' -x -f arch.tar + + 4. Convert each file name to lower case: + + $ tar --transform 's/.*/\L&/' -x -f arch.tar + + + Unlike `--strip-components', `--transform' can be used in any GNU +`tar' operation mode. For example, the following command adds files to +the archive while replacing the leading `usr/' component with `var/': + + $ tar -cf arch.tar --transform='s,^usr/,var/,' / + + To test `--transform' effect we suggest using +`--show-transformed-names' option: + + $ tar -cf arch.tar --transform='s,^usr/,var/,' \ + --verbose --show-transformed-names / + + If both `--strip-components' and `--transform' are used together, +then `--transform' is applied first, and the required number of +components is then stripped from its result. + + +File: tar.info, Node: after, Next: recurse, Prev: transform, Up: Choosing + +6.8 Operating Only on New Files +=============================== + + _(This message will disappear, once this node revised.)_ + +The `--after-date=DATE' (`--newer=DATE', `-N DATE') option causes `tar' +to only work on files whose data modification or status change times +are newer than the DATE given. If DATE starts with `/' or `.', it is +taken to be a file name; the data modification time of that file is +used as the date. If you use this option when creating or appending to +an archive, the archive will only include new files. If you use +`--after-date' when extracting an archive, `tar' will only extract +files newer than the DATE you specify. + + If you only want `tar' to make the date comparison based on +modification of the file's data (rather than status changes), then use +the `--newer-mtime=DATE' option. + + You may use these options with any operation. Note that these +options differ from the `--update' (`-u') operation in that they allow +you to specify a particular date against which `tar' can compare when +deciding whether or not to archive the files. + +`--after-date=DATE' +`--newer=DATE' +`-N DATE' + Only store files newer than DATE. + + Acts on files only if their data modification or status change + times are later than DATE. Use in conjunction with any operation. + + If DATE starts with `/' or `.', it is taken to be a file name; the + data modification time of that file is used as the date. + +`--newer-mtime=DATE' + Acts like `--after-date', but only looks at data modification + times. + + These options limit `tar' to operate only on files which have been +modified after the date specified. A file's status is considered to +have changed if its contents have been modified, or if its owner, +permissions, and so forth, have been changed. (For more information on +how to specify a date, see *note Date input formats::; remember that the +entire date argument must be quoted if it contains any spaces.) + + Gurus would say that `--after-date' tests both the data modification +time (`mtime', the time the contents of the file were last modified) +and the status change time (`ctime', the time the file's status was +last changed: owner, permissions, etc.) fields, while `--newer-mtime' +tests only the `mtime' field. + + To be precise, `--after-date' checks _both_ `mtime' and `ctime' and +processes the file if either one is more recent than DATE, while +`--newer-mtime' only checks `mtime' and disregards `ctime'. Neither +does it use `atime' (the last time the contents of the file were looked +at). + + Date specifiers can have embedded spaces. Because of this, you may +need to quote date arguments to keep the shell from parsing them as +separate arguments. For example, the following command will add to the +archive all the files modified less than two days ago: + + $ tar -cf foo.tar --newer-mtime '2 days ago' + + When any of these options is used with the option `--verbose' (*note +verbose tutorial::) GNU `tar' will try to convert the specified date +back to its textual representation and compare that with the one given +with the option. If the two dates differ, `tar' will print a warning +saying what date it will use. This is to help user ensure he is using +the right date. For example: + + $ tar -c -f archive.tar --after-date='10 days ago' . + tar: Option --after-date: Treating date `10 days ago' as 2006-06-11 + 13:19:37.232434 + + *Please Note:* `--after-date' and `--newer-mtime' should not be + used for incremental backups. *Note Incremental Dumps::, for + proper way of creating incremental backups. + + +File: tar.info, Node: recurse, Next: one, Prev: after, Up: Choosing + +6.9 Descending into Directories +=============================== + + _(This message will disappear, once this node revised.)_ + +Usually, `tar' will recursively explore all directories (either those +given on the command line or through the `--files-from' option) for the +various files they contain. However, you may not always want `tar' to +act this way. + + The `--no-recursion' option inhibits `tar''s recursive descent into +specified directories. If you specify `--no-recursion', you can use +the `find' utility for hunting through levels of directories to +construct a list of file names which you could then pass to `tar'. +`find' allows you to be more selective when choosing which files to +archive; see *note files::, for more information on using `find' with +`tar', or look. + +`--no-recursion' + Prevents `tar' from recursively descending directories. + +`--recursion' + Requires `tar' to recursively descend directories. This is the + default. + + When you use `--no-recursion', GNU `tar' grabs directory entries +themselves, but does not descend on them recursively. Many people use +`find' for locating files they want to back up, and since `tar' +_usually_ recursively descends on directories, they have to use the +`-not -type d' test in their `find' invocation (*note Type: +(find)Type.), as they usually do not want all the files in a directory. +They then use the `--files-from' option to archive the files located +via `find'. + + The problem when restoring files archived in this manner is that the +directories themselves are not in the archive; so the +`--same-permissions' (`--preserve-permissions', `-p') option does not +affect them--while users might really like it to. Specifying +`--no-recursion' is a way to tell `tar' to grab only the directory +entries given to it, adding no new files on its own. To summarize, if +you use `find' to create a list of files to be stored in an archive, +use it as follows: + + $ find DIR TESTS | \ + tar -cf ARCHIVE -T - --no-recursion + + The `--no-recursion' option also applies when extracting: it causes +`tar' to extract only the matched directory entries, not the files +under those directories. + + The `--no-recursion' option also affects how globbing patterns are +interpreted (*note controlling pattern-matching::). + + The `--no-recursion' and `--recursion' options apply to later +options and operands, and can be overridden by later occurrences of +`--no-recursion' and `--recursion'. For example: + + $ tar -cf jams.tar --no-recursion grape --recursion grape/concord + +creates an archive with one entry for `grape', and the recursive +contents of `grape/concord', but no entries under `grape' other than +`grape/concord'. + + +File: tar.info, Node: one, Prev: recurse, Up: Choosing + +6.10 Crossing File System Boundaries +==================================== + + _(This message will disappear, once this node revised.)_ + +`tar' will normally automatically cross file system boundaries in order +to archive files which are part of a directory tree. You can change +this behavior by running `tar' and specifying `--one-file-system'. +This option only affects files that are archived because they are in a +directory that is being archived; `tar' will still archive files +explicitly named on the command line or through `--files-from', +regardless of where they reside. + +`--one-file-system' + Prevents `tar' from crossing file system boundaries when + archiving. Use in conjunction with any write operation. + + The `--one-file-system' option causes `tar' to modify its normal +behavior in archiving the contents of directories. If a file in a +directory is not on the same file system as the directory itself, then +`tar' will not archive that file. If the file is a directory itself, +`tar' will not archive anything beneath it; in other words, `tar' will +not cross mount points. + + This option is useful for making full or incremental archival +backups of a file system. If this option is used in conjunction with +`--verbose' (`-v'), files that are excluded are mentioned by name on +the standard error. + +* Menu: + +* directory:: Changing Directory +* absolute:: Absolute File Names + + +File: tar.info, Node: directory, Next: absolute, Up: one + +6.10.1 Changing the Working Directory +------------------------------------- + +To change the working directory in the middle of a list of file names, +either on the command line or in a file specified using `--files-from' +(`-T'), use `--directory' (`-C'). This will change the working +directory to the specified directory after that point in the list. + +`--directory=DIRECTORY' +`-C DIRECTORY' + Changes the working directory in the middle of a command line. + + For example, + + $ tar -c -f jams.tar grape prune -C food cherry + +will place the files `grape' and `prune' from the current directory +into the archive `jams.tar', followed by the file `cherry' from the +directory `food'. This option is especially useful when you have +several widely separated files that you want to store in the same +archive. + + Note that the file `cherry' is recorded in the archive under the +precise name `cherry', _not_ `food/cherry'. Thus, the archive will +contain three files that all appear to have come from the same +directory; if the archive is extracted with plain `tar --extract', all +three files will be written in the current directory. + + Contrast this with the command, + + $ tar -c -f jams.tar grape prune -C food red/cherry + +which records the third file in the archive under the name `red/cherry' +so that, if the archive is extracted using `tar --extract', the third +file will be written in a subdirectory named `orange-colored'. + + You can use the `--directory' option to make the archive independent +of the original name of the directory holding the files. The following +command places the files `/etc/passwd', `/etc/hosts', and `/lib/libc.a' +into the archive `foo.tar': + + $ tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a + +However, the names of the archive members will be exactly what they were +on the command line: `passwd', `hosts', and `libc.a'. They will not +appear to be related by file name to the original directories where +those files were located. + + Note that `--directory' options are interpreted consecutively. If +`--directory' specifies a relative file name, it is interpreted +relative to the then current directory, which might not be the same as +the original current working directory of `tar', due to a previous +`--directory' option. + + When using `--files-from' (*note files::), you can put various `tar' +options (including `-C') in the file list. Notice, however, that in +this case the option and its argument may not be separated by +whitespace. If you use short option, its argument must either follow +the option letter immediately, without any intervening whitespace, or +occupy the next line. Otherwise, if you use long option, separate its +argument by an equal sign. + + For instance, the file list for the above example will be: + + -C/etc + passwd + hosts + --directory=/lib + libc.a + +To use it, you would invoke `tar' as follows: + + $ tar -c -f foo.tar --files-from list + + The interpretation of `--directory' is disabled by `--null' option. + + +File: tar.info, Node: absolute, Prev: directory, Up: one + +6.10.2 Absolute File Names +-------------------------- + + _(This message will disappear, once this node revised.)_ + +`--absolute-names' +`-P' + Do not strip leading slashes from file names, and permit file names + containing a `..' file name component. + + By default, GNU `tar' drops a leading `/' on input or output, and +complains about file names containing a `..' component. This option +turns off this behavior. + + When `tar' extracts archive members from an archive, it strips any +leading slashes (`/') from the member name. This causes absolute +member names in the archive to be treated as relative file names. This +allows you to have such members extracted wherever you want, instead of +being restricted to extracting the member in the exact directory named +in the archive. For example, if the archive member has the name +`/etc/passwd', `tar' will extract it as if the name were really +`etc/passwd'. + + File names containing `..' can cause problems when extracting, so +`tar' normally warns you about such files when creating an archive, and +rejects attempts to extracts such files. + + Other `tar' programs do not do this. As a result, if you create an +archive whose member names start with a slash, they will be difficult +for other people with a non-GNU `tar' program to use. Therefore, GNU +`tar' also strips leading slashes from member names when putting +members into the archive. For example, if you ask `tar' to add the file +`/bin/ls' to an archive, it will do so, but the member name will be +`bin/ls'.(1) + + If you use the `--absolute-names' (`-P') option, `tar' will do none +of these transformations. + + To archive or extract files relative to the root directory, specify +the `--absolute-names' (`-P') option. + + Normally, `tar' acts on files relative to the working +directory--ignoring superior directory names when archiving, and +ignoring leading slashes when extracting. + + When you specify `--absolute-names' (`-P'), `tar' stores file names +including all superior directory names, and preserves leading slashes. +If you only invoked `tar' from the root directory you would never need +the `--absolute-names' option, but using this option may be more +convenient than switching to root. + +`--absolute-names' + Preserves full file names (including superior directory names) when + archiving files. Preserves leading slash when extracting files. + + + `tar' prints out a message about removing the `/' from file names. +This message appears once per GNU `tar' invocation. It represents +something which ought to be told; ignoring what it means can cause very +serious surprises, later. + + Some people, nevertheless, do not want to see this message. Wanting +to play really dangerously, one may of course redirect `tar' standard +error to the sink. For example, under `sh': + + $ tar -c -f archive.tar /home 2> /dev/null + +Another solution, both nicer and simpler, would be to change to the `/' +directory first, and then avoid absolute notation. For example: + + $ (cd / && tar -c -f archive.tar home) + # or: + $ tar -c -f archive.tar -C / home + + ---------- Footnotes ---------- + + (1) A side effect of this is that when `--create' is used with +`--verbose' the resulting output is not, generally speaking, the same +as the one you'd get running `tar --list' command. This may be +important if you use some scripts for comparing both outputs. *Note +listing member and file names::, for the information on how to handle +this case. + + +File: tar.info, Node: Date input formats, Next: Formats, Prev: Choosing, Up: Top + +7 Date input formats +******************** + +First, a quote: + + Our units of temporal measurement, from seconds on up to months, + are so complicated, asymmetrical and disjunctive so as to make + coherent mental reckoning in time all but impossible. Indeed, had + some tyrannical god contrived to enslave our minds to time, to + make it all but impossible for us to escape subjection to sodden + routines and unpleasant surprises, he could hardly have done + better than handing down our present system. It is like a set of + trapezoidal building blocks, with no vertical or horizontal + surfaces, like a language in which the simplest thought demands + ornate constructions, useless particles and lengthy + circumlocutions. Unlike the more successful patterns of language + and science, which enable us to face experience boldly or at least + level-headedly, our system of temporal calculation silently and + persistently encourages our terror of time. + + ... It is as though architects had to measure length in feet, + width in meters and height in ells; as though basic instruction + manuals demanded a knowledge of five different languages. It is + no wonder then that we often look into our own immediate past or + future, last Tuesday or a week from Sunday, with feelings of + helpless confusion. ... + + -- Robert Grudin, `Time and the Art of Living'. + + This section describes the textual date representations that GNU +programs accept. These are the strings you, as a user, can supply as +arguments to the various programs. The C interface (via the `get_date' +function) is not described here. + +* Menu: + +* General date syntax:: Common rules. +* Calendar date items:: 19 Dec 1994. +* Time of day items:: 9:20pm. +* Time zone items:: EST, PDT, GMT. +* Day of week items:: Monday and others. +* Relative items in date strings:: next tuesday, 2 years ago. +* Pure numbers in date strings:: 19931219, 1440. +* Seconds since the Epoch:: @1078100502. +* Specifying time zone rules:: TZ="America/New_York", TZ="UTC0". +* Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al. + + +File: tar.info, Node: General date syntax, Next: Calendar date items, Up: Date input formats + +7.1 General date syntax +======================= + +A "date" is a string, possibly empty, containing many items separated +by whitespace. The whitespace may be omitted when no ambiguity arises. +The empty string means the beginning of today (i.e., midnight). Order +of the items is immaterial. A date string may contain many flavors of +items: + + * calendar date items + + * time of day items + + * time zone items + + * day of the week items + + * relative items + + * pure numbers. + +We describe each of these item types in turn, below. + + A few ordinal numbers may be written out in words in some contexts. +This is most useful for specifying day of the week items or relative +items (see below). Among the most commonly used ordinal numbers, the +word `last' stands for -1, `this' stands for 0, and `first' and `next' +both stand for 1. Because the word `second' stands for the unit of +time there is no way to write the ordinal number 2, but for convenience +`third' stands for 3, `fourth' for 4, `fifth' for 5, `sixth' for 6, +`seventh' for 7, `eighth' for 8, `ninth' for 9, `tenth' for 10, +`eleventh' for 11 and `twelfth' for 12. + + When a month is written this way, it is still considered to be +written numerically, instead of being "spelled in full"; this changes +the allowed strings. + + In the current implementation, only English is supported for words +and abbreviations like `AM', `DST', `EST', `first', `January', +`Sunday', `tomorrow', and `year'. + + The output of the `date' command is not always acceptable as a date +string, not only because of the language problem, but also because +there is no standard meaning for time zone items like `IST'. When using +`date' to generate a date string intended to be parsed later, specify a +date format that is independent of language and that does not use time +zone items other than `UTC' and `Z'. Here are some ways to do this: + + $ LC_ALL=C TZ=UTC0 date + Mon Mar 1 00:21:42 UTC 2004 + $ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ' + 2004-03-01 00:21:42Z + $ date --iso-8601=ns | tr T ' ' # --iso-8601 is a GNU extension. + 2004-02-29 16:21:42,692722128-0800 + $ date --rfc-2822 # a GNU extension + Sun, 29 Feb 2004 16:21:42 -0800 + $ date +'%Y-%m-%d %H:%M:%S %z' # %z is a GNU extension. + 2004-02-29 16:21:42 -0800 + $ date +'@%s.%N' # %s and %N are GNU extensions. + @1078100502.692722128 + + Alphabetic case is completely ignored in dates. Comments may be +introduced between round parentheses, as long as included parentheses +are properly nested. Hyphens not followed by a digit are currently +ignored. Leading zeros on numbers are ignored. + + Invalid dates like `2005-02-29' or times like `24:00' are rejected. +In the typical case of a host that does not support leap seconds, a +time like `23:59:60' is rejected even if it corresponds to a valid leap +second. + + +File: tar.info, Node: Calendar date items, Next: Time of day items, Prev: General date syntax, Up: Date input formats + +7.2 Calendar date items +======================= + +A "calendar date item" specifies a day of the year. It is specified +differently, depending on whether the month is specified numerically or +literally. All these strings specify the same calendar date: + + 1972-09-24 # ISO 8601. + 72-9-24 # Assume 19xx for 69 through 99, + # 20xx for 00 through 68. + 72-09-24 # Leading zeros are ignored. + 9/24/72 # Common U.S. writing. + 24 September 1972 + 24 Sept 72 # September has a special abbreviation. + 24 Sep 72 # Three-letter abbreviations always allowed. + Sep 24, 1972 + 24-sep-72 + 24sep72 + + The year can also be omitted. In this case, the last specified year +is used, or the current year if none. For example: + + 9/24 + sep 24 + + Here are the rules. + + For numeric months, the ISO 8601 format `YEAR-MONTH-DAY' is allowed, +where YEAR is any positive number, MONTH is a number between 01 and 12, +and DAY is a number between 01 and 31. A leading zero must be present +if a number is less than ten. If YEAR is 68 or smaller, then 2000 is +added to it; otherwise, if YEAR is less than 100, then 1900 is added to +it. The construct `MONTH/DAY/YEAR', popular in the United States, is +accepted. Also `MONTH/DAY', omitting the year. + + Literal months may be spelled out in full: `January', `February', +`March', `April', `May', `June', `July', `August', `September', +`October', `November' or `December'. Literal months may be abbreviated +to their first three letters, possibly followed by an abbreviating dot. +It is also permitted to write `Sept' instead of `September'. + + When months are written literally, the calendar date may be given as +any of the following: + + DAY MONTH YEAR + DAY MONTH + MONTH DAY YEAR + DAY-MONTH-YEAR + + Or, omitting the year: + + MONTH DAY + + +File: tar.info, Node: Time of day items, Next: Time zone items, Prev: Calendar date items, Up: Date input formats + +7.3 Time of day items +===================== + +A "time of day item" in date strings specifies the time on a given day. +Here are some examples, all of which represent the same time: + + 20:02:00.000000 + 20:02 + 8:02pm + 20:02-0500 # In EST (U.S. Eastern Standard Time). + + More generally, the time of day may be given as +`HOUR:MINUTE:SECOND', where HOUR is a number between 0 and 23, MINUTE +is a number between 0 and 59, and SECOND is a number between 0 and 59 +possibly followed by `.' or `,' and a fraction containing one or more +digits. Alternatively, `:SECOND' can be omitted, in which case it is +taken to be zero. On the rare hosts that support leap seconds, SECOND +may be 60. + + If the time is followed by `am' or `pm' (or `a.m.' or `p.m.'), HOUR +is restricted to run from 1 to 12, and `:MINUTE' may be omitted (taken +to be zero). `am' indicates the first half of the day, `pm' indicates +the second half of the day. In this notation, 12 is the predecessor of +1: midnight is `12am' while noon is `12pm'. (This is the zero-oriented +interpretation of `12am' and `12pm', as opposed to the old tradition +derived from Latin which uses `12m' for noon and `12pm' for midnight.) + + The time may alternatively be followed by a time zone correction, +expressed as `SHHMM', where S is `+' or `-', HH is a number of zone +hours and MM is a number of zone minutes. You can also separate HH +from MM with a colon. When a time zone correction is given this way, it +forces interpretation of the time relative to Coordinated Universal +Time (UTC), overriding any previous specification for the time zone or +the local time zone. For example, `+0530' and `+05:30' both stand for +the time zone 5.5 hours ahead of UTC (e.g., India). The MINUTE part of +the time of day may not be elided when a time zone correction is used. +This is the best way to specify a time zone correction by fractional +parts of an hour. + + Either `am'/`pm' or a time zone correction may be specified, but not +both. + + +File: tar.info, Node: Time zone items, Next: Day of week items, Prev: Time of day items, Up: Date input formats + +7.4 Time zone items +=================== + +A "time zone item" specifies an international time zone, indicated by a +small set of letters, e.g., `UTC' or `Z' for Coordinated Universal +Time. Any included periods are ignored. By following a +non-daylight-saving time zone by the string `DST' in a separate word +(that is, separated by some white space), the corresponding daylight +saving time zone may be specified. Alternatively, a +non-daylight-saving time zone can be followed by a time zone +correction, to add the two values. This is normally done only for +`UTC'; for example, `UTC+05:30' is equivalent to `+05:30'. + + Time zone items other than `UTC' and `Z' are obsolescent and are not +recommended, because they are ambiguous; for example, `EST' has a +different meaning in Australia than in the United States. Instead, +it's better to use unambiguous numeric time zone corrections like +`-0500', as described in the previous section. + + If neither a time zone item nor a time zone correction is supplied, +time stamps are interpreted using the rules of the default time zone +(*note Specifying time zone rules::). + + +File: tar.info, Node: Day of week items, Next: Relative items in date strings, Prev: Time zone items, Up: Date input formats + +7.5 Day of week items +===================== + +The explicit mention of a day of the week will forward the date (only +if necessary) to reach that day of the week in the future. + + Days of the week may be spelled out in full: `Sunday', `Monday', +`Tuesday', `Wednesday', `Thursday', `Friday' or `Saturday'. Days may +be abbreviated to their first three letters, optionally followed by a +period. The special abbreviations `Tues' for `Tuesday', `Wednes' for +`Wednesday' and `Thur' or `Thurs' for `Thursday' are also allowed. + + A number may precede a day of the week item to move forward +supplementary weeks. It is best used in expression like `third +monday'. In this context, `last DAY' or `next DAY' is also acceptable; +they move one week before or after the day that DAY by itself would +represent. + + A comma following a day of the week item is ignored. + + +File: tar.info, Node: Relative items in date strings, Next: Pure numbers in date strings, Prev: Day of week items, Up: Date input formats + +7.6 Relative items in date strings +================================== + +"Relative items" adjust a date (or the current date if none) forward or +backward. The effects of relative items accumulate. Here are some +examples: + + 1 year + 1 year ago + 3 years + 2 days + + The unit of time displacement may be selected by the string `year' +or `month' for moving by whole years or months. These are fuzzy units, +as years and months are not all of equal duration. More precise units +are `fortnight' which is worth 14 days, `week' worth 7 days, `day' +worth 24 hours, `hour' worth 60 minutes, `minute' or `min' worth 60 +seconds, and `second' or `sec' worth one second. An `s' suffix on +these units is accepted and ignored. + + The unit of time may be preceded by a multiplier, given as an +optionally signed number. Unsigned numbers are taken as positively +signed. No number at all implies 1 for a multiplier. Following a +relative item by the string `ago' is equivalent to preceding the unit +by a multiplier with value -1. + + The string `tomorrow' is worth one day in the future (equivalent to +`day'), the string `yesterday' is worth one day in the past (equivalent +to `day ago'). + + The strings `now' or `today' are relative items corresponding to +zero-valued time displacement, these strings come from the fact a +zero-valued time displacement represents the current time when not +otherwise changed by previous items. They may be used to stress other +items, like in `12:00 today'. The string `this' also has the meaning +of a zero-valued time displacement, but is preferred in date strings +like `this thursday'. + + When a relative item causes the resulting date to cross a boundary +where the clocks were adjusted, typically for daylight saving time, the +resulting date and time are adjusted accordingly. + + The fuzz in units can cause problems with relative items. For +example, `2003-07-31 -1 month' might evaluate to 2003-07-01, because +2003-06-31 is an invalid date. To determine the previous month more +reliably, you can ask for the month before the 15th of the current +month. For example: + + $ date -R + Thu, 31 Jul 2003 13:02:39 -0700 + $ date --date='-1 month' +'Last month was %B?' + Last month was July? + $ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!' + Last month was June! + + Also, take care when manipulating dates around clock changes such as +daylight saving leaps. In a few cases these have added or subtracted +as much as 24 hours from the clock, so it is often wise to adopt +universal time by setting the `TZ' environment variable to `UTC0' +before embarking on calendrical calculations. + + +File: tar.info, Node: Pure numbers in date strings, Next: Seconds since the Epoch, Prev: Relative items in date strings, Up: Date input formats + +7.7 Pure numbers in date strings +================================ + +The precise interpretation of a pure decimal number depends on the +context in the date string. + + If the decimal number is of the form YYYYMMDD and no other calendar +date item (*note Calendar date items::) appears before it in the date +string, then YYYY is read as the year, MM as the month number and DD as +the day of the month, for the specified calendar date. + + If the decimal number is of the form HHMM and no other time of day +item appears before it in the date string, then HH is read as the hour +of the day and MM as the minute of the hour, for the specified time of +day. MM can also be omitted. + + If both a calendar date and a time of day appear to the left of a +number in the date string, but no relative item, then the number +overrides the year. + + +File: tar.info, Node: Seconds since the Epoch, Next: Specifying time zone rules, Prev: Pure numbers in date strings, Up: Date input formats + +7.8 Seconds since the Epoch +=========================== + +If you precede a number with `@', it represents an internal time stamp +as a count of seconds. The number can contain an internal decimal +point (either `.' or `,'); any excess precision not supported by the +internal representation is truncated toward minus infinity. Such a +number cannot be combined with any other date item, as it specifies a +complete time stamp. + + Internally, computer times are represented as a count of seconds +since an epoch--a well-defined point of time. On GNU and POSIX +systems, the epoch is 1970-01-01 00:00:00 UTC, so `@0' represents this +time, `@1' represents 1970-01-01 00:00:01 UTC, and so forth. GNU and +most other POSIX-compliant systems support such times as an extension +to POSIX, using negative counts, so that `@-1' represents 1969-12-31 +23:59:59 UTC. + + Traditional Unix systems count seconds with 32-bit two's-complement +integers and can represent times from 1901-12-13 20:45:52 through +2038-01-19 03:14:07 UTC. More modern systems use 64-bit counts of +seconds with nanosecond subcounts, and can represent all the times in +the known lifetime of the universe to a resolution of 1 nanosecond. + + On most hosts, these counts ignore the presence of leap seconds. +For example, on most hosts `@915148799' represents 1998-12-31 23:59:59 +UTC, `@915148800' represents 1999-01-01 00:00:00 UTC, and there is no +way to represent the intervening leap second 1998-12-31 23:59:60 UTC. + + +File: tar.info, Node: Specifying time zone rules, Next: Authors of get_date, Prev: Seconds since the Epoch, Up: Date input formats + +7.9 Specifying time zone rules +============================== + +Normally, dates are interpreted using the rules of the current time +zone, which in turn are specified by the `TZ' environment variable, or +by a system default if `TZ' is not set. To specify a different set of +default time zone rules that apply just to one date, start the date +with a string of the form `TZ="RULE"'. The two quote characters (`"') +must be present in the date, and any quotes or backslashes within RULE +must be escaped by a backslash. + + For example, with the GNU `date' command you can answer the question +"What time is it in New York when a Paris clock shows 6:30am on October +31, 2004?" by using a date beginning with `TZ="Europe/Paris"' as shown +in the following shell transcript: + + $ export TZ="America/New_York" + $ date --date='TZ="Europe/Paris" 2004-10-31 06:30' + Sun Oct 31 01:30:00 EDT 2004 + + In this example, the `--date' operand begins with its own `TZ' +setting, so the rest of that operand is processed according to +`Europe/Paris' rules, treating the string `2004-10-31 06:30' as if it +were in Paris. However, since the output of the `date' command is +processed according to the overall time zone rules, it uses New York +time. (Paris was normally six hours ahead of New York in 2004, but +this example refers to a brief Halloween period when the gap was five +hours.) + + A `TZ' value is a rule that typically names a location in the `tz' +database (http://www.twinsun.com/tz/tz-link.htm). A recent catalog of +location names appears in the TWiki Date and Time Gateway +(http://twiki.org/cgi-bin/xtra/tzdate). A few non-GNU hosts require a +colon before a location name in a `TZ' setting, e.g., +`TZ=":America/New_York"'. + + The `tz' database includes a wide variety of locations ranging from +`Arctic/Longyearbyen' to `Antarctica/South_Pole', but if you are at sea +and have your own private time zone, or if you are using a non-GNU host +that does not support the `tz' database, you may need to use a POSIX +rule instead. Simple POSIX rules like `UTC0' specify a time zone +without daylight saving time; other rules can specify simple daylight +saving regimes. *Note Specifying the Time Zone with `TZ': (libc)TZ +Variable. + + +File: tar.info, Node: Authors of get_date, Prev: Specifying time zone rules, Up: Date input formats + +7.10 Authors of `get_date' +========================== + +`get_date' was originally implemented by Steven M. Bellovin +(<smb@research.att.com>) while at the University of North Carolina at +Chapel Hill. The code was later tweaked by a couple of people on +Usenet, then completely overhauled by Rich $alz (<rsalz@bbn.com>) and +Jim Berets (<jberets@bbn.com>) in August, 1990. Various revisions for +the GNU system were made by David MacKenzie, Jim Meyering, Paul Eggert +and others. + + This chapter was originally produced by Franc,ois Pinard +(<pinard@iro.umontreal.ca>) from the `getdate.y' source code, and then +edited by K. Berry (<kb@cs.umb.edu>). + + +File: tar.info, Node: Formats, Next: Media, Prev: Date input formats, Up: Top + +8 Controlling the Archive Format +******************************** + +Due to historical reasons, there are several formats of tar archives. +All of them are based on the same principles, but have some subtle +differences that often make them incompatible with each other. + + GNU tar is able to create and handle archives in a variety of +formats. The most frequently used formats are (in alphabetical order): + +gnu + Format used by GNU `tar' versions up to 1.13.25. This format + derived from an early POSIX standard, adding some improvements + such as sparse file handling and incremental archives. + Unfortunately these features were implemented in a way + incompatible with other archive formats. + + Archives in `gnu' format are able to hold file names of unlimited + length. + +oldgnu + Format used by GNU `tar' of versions prior to 1.12. + +v7 + Archive format, compatible with the V7 implementation of tar. This + format imposes a number of limitations. The most important of them + are: + + 1. The maximum length of a file name is limited to 99 characters. + + 2. The maximum length of a symbolic link is limited to 99 + characters. + + 3. It is impossible to store special files (block and character + devices, fifos etc.) + + 4. Maximum value of user or group ID is limited to 2097151 + (7777777 octal) + + 5. V7 archives do not contain symbolic ownership information + (user and group name of the file owner). + + This format has traditionally been used by Automake when producing + Makefiles. This practice will change in the future, in the + meantime, however this means that projects containing file names + more than 99 characters long will not be able to use GNU `tar' + 1.17 and Automake prior to 1.9. + +ustar + Archive format defined by POSIX.1-1988 specification. It stores + symbolic ownership information. It is also able to store special + files. However, it imposes several restrictions as well: + + 1. The maximum length of a file name is limited to 256 + characters, provided that the file name can be split at a + directory separator in two parts, first of them being at most + 155 bytes long. So, in most cases the maximum file name + length will be shorter than 256 characters. + + 2. The maximum length of a symbolic link name is limited to 100 + characters. + + 3. Maximum size of a file the archive is able to accommodate is + 8GB + + 4. Maximum value of UID/GID is 2097151. + + 5. Maximum number of bits in device major and minor numbers is + 21. + +star + Format used by Jo"rg Schilling `star' implementation. GNU `tar' + is able to read `star' archives but currently does not produce + them. + +posix + Archive format defined by POSIX.1-2001 specification. This is the + most flexible and feature-rich format. It does not impose any + restrictions on file sizes or file name lengths. This format is + quite recent, so not all tar implementations are able to handle it + properly. However, this format is designed in such a way that any + tar implementation able to read `ustar' archives will be able to + read most `posix' archives as well, with the only exception that + any additional information (such as long file names etc.) will in + such case be extracted as plain text files along with the files it + refers to. + + This archive format will be the default format for future versions + of GNU `tar'. + + + The following table summarizes the limitations of each of these +formats: + +Format UID File Size File Name Devn +-------------------------------------------------------------------- +gnu 1.8e19 Unlimited Unlimited 63 +oldgnu 1.8e19 Unlimited Unlimited 63 +v7 2097151 8GB 99 n/a +ustar 2097151 8GB 256 21 +posix Unlimited Unlimited Unlimited Unlimited + + The default format for GNU `tar' is defined at compilation time. +You may check it by running `tar --help', and examining the last lines +of its output. Usually, GNU `tar' is configured to create archives in +`gnu' format, however, future version will switch to `posix'. + +* Menu: + +* Compression:: Using Less Space through Compression +* Attributes:: Handling File Attributes +* Portability:: Making `tar' Archives More Portable +* cpio:: Comparison of `tar' and `cpio' + + +File: tar.info, Node: Compression, Next: Attributes, Up: Formats + +8.1 Using Less Space through Compression +======================================== + +* Menu: + +* gzip:: Creating and Reading Compressed Archives +* sparse:: Archiving Sparse Files + + +File: tar.info, Node: gzip, Next: sparse, Up: Compression + +8.1.1 Creating and Reading Compressed Archives +---------------------------------------------- + +GNU `tar' is able to create and read compressed archives. It supports +`gzip' and `bzip2' compression programs. For backward compatibility, +it also supports `compress' command, although we strongly recommend +against using it, since there is a patent covering the algorithm it +uses and you could be sued for patent infringement merely by running +`compress'! Besides, it is less effective than `gzip' and `bzip2'. + + Creating a compressed archive is simple: you just specify a +"compression option" along with the usual archive creation commands. +The compression option is `-z' (`--gzip') to create a `gzip' compressed +archive, `-j' (`--bzip2') to create a `bzip2' compressed archive, and +`-Z' (`--compress') to use `compress' program. For example: + + $ tar cfz archive.tar.gz . + + Reading compressed archive is even simpler: you don't need to specify +any additional options as GNU `tar' recognizes its format +automatically. Thus, the following commands will list and extract the +archive created in previous example: + + # List the compressed archive + $ tar tf archive.tar.gz + # Extract the compressed archive + $ tar xf archive.tar.gz + + The only case when you have to specify a decompression option while +reading the archive is when reading from a pipe or from a tape drive +that does not support random access. However, in this case GNU `tar' +will indicate which option you should use. For example: + + $ cat archive.tar.gz | tar tf - + tar: Archive is compressed. Use -z option + tar: Error is not recoverable: exiting now + + If you see such diagnostics, just add the suggested option to the +invocation of GNU `tar': + + $ cat archive.tar.gz | tar tfz - + + Notice also, that there are several restrictions on operations on +compressed archives. First of all, compressed archives cannot be +modified, i.e., you cannot update (`--update' (`-u')) them or delete +(`--delete') members from them. Likewise, you cannot append another +`tar' archive to a compressed archive using `--append' (`-r')). +Secondly, multi-volume archives cannot be compressed. + + The following table summarizes compression options used by GNU `tar'. + +`-z' +`--gzip' +`--ungzip' + Filter the archive through `gzip'. + + You can use `--gzip' and `--gunzip' on physical devices (tape + drives, etc.) and remote files as well as on normal files; data to + or from such devices or remote files is reblocked by another copy + of the `tar' program to enforce the specified (or default) record + size. The default compression parameters are used; if you need to + override them, set `GZIP' environment variable, e.g.: + + $ GZIP=--best tar cfz archive.tar.gz subdir + + Another way would be to avoid the `--gzip' (`--gunzip', + `--ungzip', `-z') option and run `gzip' explicitly: + + $ tar cf - subdir | gzip --best -c - > archive.tar.gz + + About corrupted compressed archives: `gzip''ed files have no + redundancy, for maximum compression. The adaptive nature of the + compression scheme means that the compression tables are implicitly + spread all over the archive. If you lose a few blocks, the dynamic + construction of the compression tables becomes unsynchronized, and + there is little chance that you could recover later in the archive. + + There are pending suggestions for having a per-volume or per-file + compression in GNU `tar'. This would allow for viewing the + contents without decompression, and for resynchronizing + decompression at every volume or file, in case of corrupted + archives. Doing so, we might lose some compressibility. But this + would have make recovering easier. So, there are pros and cons. + We'll see! + +`-j' +`--bzip2' + Filter the archive through `bzip2'. Otherwise like `--gzip'. + +`-Z' +`--compress' +`--uncompress' + Filter the archive through `compress'. Otherwise like `--gzip'. + + The GNU Project recommends you not use `compress', because there + is a patent covering the algorithm it uses. You could be sued for + patent infringement merely by running `compress'. + +`--use-compress-program=PROG' + Use external compression program PROG. Use this option if you + have a compression program that GNU `tar' does not support. There + are two requirements to which PROG should comply: + + First, when called without options, it should read data from + standard input, compress it and output it on standard output. + + Secondly, if called with `-d' argument, it should do exactly the + opposite, i.e., read the compressed data from the standard input + and produce uncompressed data on the standard output. + + The `--use-compress-program' option, in particular, lets you +implement your own filters, not necessarily dealing with +compression/decompression. For example, suppose you wish to implement +PGP encryption on top of compression, using `gpg' (*note gpg: +(gpg)Top.). The following script does that: + + #! /bin/sh + case $1 in + -d) gpg --decrypt - | gzip -d -c;; + '') gzip -c | gpg -s ;; + *) echo "Unknown option $1">&2; exit 1;; + esac + + Suppose you name it `gpgz' and save it somewhere in your `PATH'. +Then the following command will create a compressed archive signed with +your private key: + + $ tar -cf foo.tar.gpgz --use-compress=gpgz . + +Likewise, the following command will list its contents: + + $ tar -tf foo.tar.gpgz --use-compress=gpgz . + + +File: tar.info, Node: sparse, Prev: gzip, Up: Compression + +8.1.2 Archiving Sparse Files +---------------------------- + +Files in the file system occasionally have "holes". A "hole" in a file +is a section of the file's contents which was never written. The +contents of a hole reads as all zeros. On many operating systems, +actual disk storage is not allocated for holes, but they are counted in +the length of the file. If you archive such a file, `tar' could create +an archive longer than the original. To have `tar' attempt to +recognize the holes in a file, use `--sparse' (`-S'). When you use +this option, then, for any file using less disk space than would be +expected from its length, `tar' searches the file for consecutive +stretches of zeros. It then records in the archive for the file where +the consecutive stretches of zeros are, and only archives the "real +contents" of the file. On extraction (using `--sparse' is not needed +on extraction) any such files have holes created wherever the +continuous stretches of zeros were found. Thus, if you use `--sparse', +`tar' archives won't take more space than the original. + +`-S' +`--sparse' + This option instructs `tar' to test each file for sparseness + before attempting to archive it. If the file is found to be + sparse it is treated specially, thus allowing to decrease the + amount of space used by its image in the archive. + + This option is meaningful only when creating or updating archives. + It has no effect on extraction. + + Consider using `--sparse' when performing file system backups, to +avoid archiving the expanded forms of files stored sparsely in the +system. + + Even if your system has no sparse files currently, some may be +created in the future. If you use `--sparse' while making file system +backups as a matter of course, you can be assured the archive will +never take more space on the media than the files take on disk +(otherwise, archiving a disk filled with sparse files might take +hundreds of tapes). *Note Incremental Dumps::. + + However, be aware that `--sparse' option presents a serious +drawback. Namely, in order to determine if the file is sparse `tar' +has to read it before trying to archive it, so in total the file is +read *twice*. So, always bear in mind that the time needed to process +all files with this option is roughly twice the time needed to archive +them without it. + + When using `POSIX' archive format, GNU `tar' is able to store sparse +files using in three distinct ways, called "sparse formats". A sparse +format is identified by its "number", consisting, as usual of two +decimal numbers, delimited by a dot. By default, format `1.0' is used. +If, for some reason, you wish to use an earlier format, you can select +it using `--sparse-version' option. + +`--sparse-version=VERSION' + Select the format to store sparse files in. Valid VERSION values + are: `0.0', `0.1' and `1.0'. *Note Sparse Formats::, for a + detailed description of each format. + + Using `--sparse-format' option implies `--sparse'. + + +File: tar.info, Node: Attributes, Next: Portability, Prev: Compression, Up: Formats + +8.2 Handling File Attributes +============================ + + _(This message will disappear, once this node revised.)_ + +When `tar' reads files, it updates their access times. To avoid this, +use the `--atime-preserve[=METHOD]' option, which can either reset the +access time retroactively or avoid changing it in the first place. + + Handling of file attributes + +`--atime-preserve' +`--atime-preserve=replace' +`--atime-preserve=system' + Preserve the access times of files that are read. This works only + for files that you own, unless you have superuser privileges. + + `--atime-preserve=replace' works on most systems, but it also + restores the data modification time and updates the status change + time. Hence it doesn't interact with incremental dumps nicely + (*note Incremental Dumps::), and it can set access or data + modification times incorrectly if other programs access the file + while `tar' is running. + + `--atime-preserve=system' avoids changing the access time in the + first place, if the operating system supports this. + Unfortunately, this may or may not work on any given operating + system or file system. If `tar' knows for sure it won't work, it + complains right away. + + Currently `--atime-preserve' with no operand defaults to + `--atime-preserve=replace', but this is intended to change to + `--atime-preserve=system' when the latter is better-supported. + +`-m' +`--touch' + Do not extract data modification time. + + When this option is used, `tar' leaves the data modification times + of the files it extracts as the times when the files were + extracted, instead of setting it to the times recorded in the + archive. + + This option is meaningless with `--list' (`-t'). + +`--same-owner' + Create extracted files with the same ownership they have in the + archive. + + This is the default behavior for the superuser, so this option is + meaningful only for non-root users, when `tar' is executed on + those systems able to give files away. This is considered as a + security flaw by many people, at least because it makes quite + difficult to correctly account users for the disk space they + occupy. Also, the `suid' or `sgid' attributes of files are easily + and silently lost when files are given away. + + When writing an archive, `tar' writes the user ID and user name + separately. If it can't find a user name (because the user ID is + not in `/etc/passwd'), then it does not write one. When restoring, + it tries to look the name (if one was written) up in + `/etc/passwd'. If it fails, then it uses the user ID stored in + the archive instead. + +`--no-same-owner' +`-o' + Do not attempt to restore ownership when extracting. This is the + default behavior for ordinary users, so this option has an effect + only for the superuser. + +`--numeric-owner' + The `--numeric-owner' option allows (ANSI) archives to be written + without user/group name information or such information to be + ignored when extracting. It effectively disables the generation + and/or use of user/group name information. This option forces + extraction using the numeric ids from the archive, ignoring the + names. + + This is useful in certain circumstances, when restoring a backup + from an emergency floppy with different passwd/group files for + example. It is otherwise impossible to extract files with the + right ownerships if the password file in use during the extraction + does not match the one belonging to the file system(s) being + extracted. This occurs, for example, if you are restoring your + files after a major crash and had booted from an emergency floppy + with no password file or put your disk into another machine to do + the restore. + + The numeric ids are _always_ saved into `tar' archives. The + identifying names are added at create time when provided by the + system, unless `--old-archive' (`-o') is used. Numeric ids could + be used when moving archives between a collection of machines using + a centralized management for attribution of numeric ids to users + and groups. This is often made through using the NIS capabilities. + + When making a `tar' file for distribution to other sites, it is + sometimes cleaner to use a single owner for all files in the + distribution, and nicer to specify the write permission bits of the + files as stored in the archive independently of their actual value + on the file system. The way to prepare a clean distribution is + usually to have some Makefile rule creating a directory, copying + all needed files in that directory, then setting ownership and + permissions as wanted (there are a lot of possible schemes), and + only then making a `tar' archive out of this directory, before + cleaning everything out. Of course, we could add a lot of options + to GNU `tar' for fine tuning permissions and ownership. This is + not the good way, I think. GNU `tar' is already crowded with + options and moreover, the approach just explained gives you a + great deal of control already. + +`-p' +`--same-permissions' +`--preserve-permissions' + Extract all protection information. + + This option causes `tar' to set the modes (access permissions) of + extracted files exactly as recorded in the archive. If this option + is not used, the current `umask' setting limits the permissions on + extracted files. This option is by default enabled when `tar' is + executed by a superuser. + + This option is meaningless with `--list' (`-t'). + +`--preserve' + Same as both `--same-permissions' and `--same-order'. + + The `--preserve' option has no equivalent short option name. It + is equivalent to `--same-permissions' plus `--same-order'. + + |